<PAGE>
 
                                                                 Exhibit 10.6(d)


                                                                [Execution Copy]


                      AMENDMENT NO. 3 TO CREDIT AGREEMENT


          AMENDMENT NO. 3 TO CREDIT AGREEMENT dated as of January 26, 1999,
between MEDIACOM SOUTHEAST LLC, a Delaware limited liability company (the
"Borrower"); each of the lenders that is a signatory hereto identified under the
 --------
caption "LENDERS" on the signature pages hereto (each, individually, a "Lender"
                                                                        ------
and, collectively, the "Lenders") and The Chase Manhattan Bank, as
                        -------
Administrative Agent (the "Administrative Agent").
                           --------------------

          The Borrower, the Lenders and the Administrative Agent, are party to a
Credit Agreement dated as of January 23, 1998 (as heretofore modified and
supplemented and in effect on the date hereof, the "Credit Agreement"),
                                                    ----------------
providing, subject to the terms and conditions thereof, for extensions of credit
in an aggregate principal amount up to but not exceeding $225,000,000 (which
may, in certain circumstances, be increased to $275,000,000). The Borrower
wishes to increase the Revolving Credit Commitments under the Credit Agreement
from $165,000,000 to $225,000,000 concurrently with a prepayment of the Term
Loans in an amount equal to such increase and to amend the Credit Agreement in
certain other respects. The Lenders and the Administrative Agent are willing to
so agree, and accordingly, the parties hereto hereby agree as follows:

          Section 1.  Definitions.  Except as otherwise defined in this
                      -----------
Amendment No. 3, terms defined in the Credit Agreement are used herein as
defined therein.

          Section 2.  Amendments.  Subject to the satisfaction of the conditions
                      ----------                                                
precedent specified in Section 5 below, but effective as of the date hereof, the
Credit Agreement shall be amended as follows:

          2.01.  References in the Credit Agreement (including references to the
Credit Agreement as amended hereby) to "this Agreement" (and indirect references
such as "hereunder", "hereby", "herein" and "hereof") shall be deemed to be
references to the Credit Agreement as amended hereby.

          2.02.  Section 1.01 of the Credit Agreement shall be amended by adding
the following new definitions (to the extent not already included in said
Section 1.01) and inserting the same in the appropriate alphabetical locations
and amending in their entirety the following definitions (to the extent already
included in said Section 1.01), as follows:

          "Amendment No. 3" shall mean Amendment No. 3 hereto dated as of
           ---------------
     January 26, 1999 between the Borrower, the Lenders and the Administrative
     Agent.

                     Amendment No. 3 to Credit Agreement 
                     -----------------------------------
<PAGE>
 
                                      -2-



          "Amendment No. 3 Effective Date" shall mean the date upon which the
           ------------------------------
     amendments provided for in Section 2 of Amendment No. 3 hereto shall become
     effective.

          "Revolving Credit Commitment" shall mean, as to each Revolving Credit
           ---------------------------
     Lender, the obligation of such Lender to make Revolving Credit Loans, and
     to issue or participate in Letters of Credit pursuant to Section 2.03
     hereof, in an aggregate principal amount at any one time outstanding up to
     but not exceeding the amount set forth opposite the name of such Lender on
     Schedule 1 to Amendment No. 3 or, in the case of a Person that becomes a
     Revolving Credit Lender pursuant to an assignment permitted under Section
     11.06(b) hereof, as specified in the respective instrument of assignment
     pursuant to which such assignment is effected (as the same may be reduced
     from time to time pursuant to Section 2.04 or 2.10 hereof, or increased or
     reduced in connection with any assignment pursuant to Section 11.06(b)
     hereof). The original aggregate principal amount of the Revolving Credit
     Commitments (after giving effect to Amendment No. 3) is $225,000,000.

          2.03.  Section 2.01 of the Credit Agreement is hereby amended by
inserting a new paragraph (f) at the end thereof to read as follows:

          "(f)  Amendment No. 3 Effective Date.  On the Amendment No. 3
                ------------------------------
     Effective Date, all of the outstanding Term Loans shall be prepaid be in
     full by the Borrower as provided in Section 5(ii) of Amendment No. 3
     hereto. Following such prepayment, all references in this Agreement to
     "Term Loans", "Term Loan Lenders" and the like shall be deemed to be
     inoperative."

          2.04.  The schedule set forth in Section 2.04(a) of the Credit
Agreement is hereby amended in its entirety to read as follows:

<TABLE>
<CAPTION>
             (A)                              (B)                             (C)
       Revolving Credit                Revolving Credit                Revolving Credit
     Commitment Reduction             Commitments Reduced             Commitments Reduced
      Date Falling on or               by the Following                to the Following
         Nearest to:                       Amounts:                        Amounts:
         ----------                        -------                         -------              
<S>                                      <C>                              <C>
     March 31, 2001                      $ 2,750,000                      $222,250,000
     June 30, 2001                       $ 2,750,000                      $219,500,000
     September 30, 2001                  $ 2,750,000                      $216,750,000
     December 31, 2001                   $ 2,750,000                      $214,000,000
</TABLE> 

                     Amendment No. 3 to Credit Agreement 
                     -----------------------------------
<PAGE>
 
                                      -3-

<TABLE> 
<CAPTION> 
<S>                                      <C>                              <C>
     March 31, 2002                      $ 5,375,000                      $208,625,000
     June 30, 2002                       $ 5,375,000                      $203,250,000
     September 30, 2002                  $ 5,375,000                      $197,875,000
     December 31, 2002                   $ 5,375,000                      $192,500,000
                                                                        
     March 31, 2003                      $ 8,750,000                      $183,750,000
     June 30, 2003                       $ 8,750,000                      $175,000,000
     September 30, 2003                  $ 8,750,000                      $166,250,000
     December 31, 2003                   $ 8,750,000                      $157,500,000
                                                                        
     March 31, 2004                      $11,500,000                      $146,000,000
     June 30, 2004                       $11,500,000                      $134,500,000
     September 30, 2004                  $11,500,000                      $123,000,000
     December 31, 2004                   $11,500,000                      $111,500,000
                                                                        
     March 31, 2005                      $13,750,000                      $ 97,750,000
     June 30, 2005                       $13,750,000                      $ 84,000,000
     September 30, 2005                  $13,750,000                      $ 70,250,000
     December 31, 2005                   $13,750,000                      $ 56,500,000
                                                                        
     March 31, 2006                      $28,250,000                      $ 28,250,000
     June 30, 2006                       $28,250,000                      $          0
</TABLE>

          2.05.  Section 8.13 of the Credit Agreement shall be amended in its
entirety to read as follows:

          "8.13  Interest Rate Protection Agreements.  The Borrower will within
                 -----------------------------------
     90 days of the Closing Date, enter into, and thereafter maintain in full
     force and effect, one or more Interest Rate Protection Agreements with one
     or more of the Lenders or their affiliates (and/or with a bank or other
     financial institution having capital, surplus and undivided profits of at
     least $500,000,000), that effectively enables the Borrower (in a manner
     satisfactory to the Majority Lenders) to protect itself, in a manner and on
     terms reasonably satisfactory to the Majority Lenders, against adverse
     fluctuations in the three-month London interbank offered rates as to a
     notional principal amount which, together with that portion of the
     aggregate outstanding principal amount of Indebtedness of the Borrower
     bearing a fixed rate of interest and the aggregate amount of the Preferred
     Membership Interests, shall in the aggregate be at least equal to 40% of
     the sum of (x) the aggregate outstanding principal amount of the
     Indebtedness (including Affiliate Subordinated Indebtedness) of the
     Borrower and (y) the aggregate amount of the Preferred Membership
     Interests."

          Section 3.  Consent.  Subject to the satisfaction of the conditions
                      -------
precedent specified in Section 5 below, but effective as of the date hereof, the
Lenders hereby consent to the amendment of the instruments and other documents
evidencing or relating to Affiliate 

                     Amendment No. 3 to Credit Agreement 
                     -----------------------------------
<PAGE>
 
                                      -4-

Subordinated Indebtedness to permit the rate of interest payable in respect
thereof to be equal to a rate of interest payable by Mediacom on its 8-1/2%
Senior Notes due 2008.

          Section 4.  Representations and Warranties.  The Borrower represents
                      ------------------------------
and warrants to the Lenders that the representations and warranties set forth in
Section 7 of the Credit Agreement are true and complete on the date hereof as if
made on and as of the date hereof and as if each reference in said Section 7 to
"this Agreement" and "the Notes" included reference to this Amendment No. 3 and
to the New Notes (as defined herein below).

          Section 5.  Conditions Precedent.  The effectiveness of the amendments
                      --------------------
set forth in Section 2 above, and the consent set forth in Section 3 above, is
subject to: (i) the condition that this Amendment No. 3 shall have been executed
and delivered by the Borrower, each Lender and the Administrative Agent (and
that Mediacom shall have executed and delivered its confirmation and consent
provided for on the signature pages hereto), in each case on or before February
15, 1999, (ii) the prepayment, in accordance with the provisions of Section 2.09
of the Credit Agreement, of Term Loans in an aggregate amount of $60,000,000
(which amount is the aggregate principal amount of Term Loans outstanding on the
date hereof) together with the payment of all interest accrued thereon in
accordance with the provisions of Section 3.02 of the Credit Agreement (and any
amounts that may be payable under Section 5.05 of the Credit Agreement in
connection therewith), which prepayment may be made from any source, including
from the increase in Revolving Credit Commitments contemplated hereby, and (iii)
the receipt by the Administrative Agent of the following documents, each of
which shall be satisfactory to the Administrative Agent (and to the extent
specified below, to each Lender or the Majority Lenders) in form and substance:

          (a)  New Notes.  A new promissory note for each Revolving Credit
               --------- 
     Lender, delivered by the Borrower in exchange for the Revolving Credit Note
     heretofore delivered to such Revolving Credit Lender, in substantially the
     form of Exhibit A-1 to the Credit Agreement, dated the date of the
     Revolving Credit Note being exchanged, payable to such Revolving Credit
     Lender in a principal amount equal to its Revolving Credit Commitment (as
     increased hereby) and otherwise duly completed. Each such promissory note
     (a "New Note") shall constitute a "Revolving Credit Note" under the Credit
         --------
     Agreement as amended hereby.

          (b)  Organizational Matters.  The Administrative Agent shall have
               ----------------------
     received such documents and certificates as the Administrative Agent or as
     Milbank, Tweed, Hadley & McCloy, special New York counsel to Chase, may
     reasonably request relating to the organization, existence and good
     standing of each Credit Party and the authorization of this Amendment No.
     3, all in form and substance reasonably satisfactory to the Administrative
     Agent and its counsel.

          (c)  Opinion of Counsel to the Obligors.  The Administrative Agent
               ----------------------------------                           
     shall have received a favorable written opinion (addressed to the
     Administrative Agent and the Lenders and dated the Amendment No. 3
     Effective Date) of Cooperman, Levitt, 

                     Amendment No. 3 to Credit Agreement 
                     -----------------------------------
<PAGE>
 
                                      -5-

     Winnikoff, Lester & Newman, P.C., counsel to the Obligors, substantially in
     the form of Exhibit A, and covering such other matters relating to the
     Obligors, this Agreement or the other Loan Documents as the Administrative
     Agent or any Lender shall reasonably request (and each Obligor hereby
     requests such counsel to deliver such opinion).


          (d)  Opinion of Special Counsel.  The Administrative Agent shall have
               --------------------------
     received a favorable written legal opinion (addressed to the Administrative
     Agent and the Lenders and dated the Effective Date) of Milbank, Tweed,
     Hadley & McCloy, special New York counsel to Chase, substantially in the
     form of Exhibit B (and the Administrative Agent hereby requests Special
     Counsel to deliver such opinion).

          (e)  Other Documents.  Such other documents as either the
               ---------------
     Administrative Agent or any Lender or Special Counsel may reasonably
     request.

          Section 6.  Confirmation of Security.  The Borrower hereby confirms
                      ------------------------
that the obligations of the Borrower under the Credit Agreement, as amended by
this Amendment No. 3, shall be entitled to the benefits of the collateral
security provided for pursuant to the Security Agreement.

          Section 7.  Miscellaneous.  Except as herein provided, the Credit
                      -------------
Agreement shall remain unchanged and in full force and effect. This Amendment
No. 3 may be executed in any number of counterparts, all of which taken together
shall constitute one and the same amendatory instrument and any of the parties
hereto may execute this Amendment No. 3 by signing any such counterpart. This
Amendment No. 3 shall be governed by, and construed in accordance with, the law
of the State of New York.

                     Amendment No. 3 to Credit Agreement 
                     -----------------------------------
<PAGE>
 
                                      -6-

          IN WITNESS WHEREOF, the parties hereto have caused this Amendment No.
3 to be duly executed and delivered as of the day and year first above written.


                                    MEDIACOM SOUTHEAST LLC



                                    By  /s/ MARK E. STEPHAN
                                      ---------------------------------------
                                     Title: Chief Financial Officer


                                    LENDERS
                                    -------
                                        

THE CHASE MANHATTAN BANK,                      BANK OF MONTREAL
 individually and as Administrative Agent


By /s/ CONSTANCE M. COHEN                      By /s/ ALLEGRA GRIFFITHS
  --------------------------                     -------------------------------
 Title: Vice President                           Title: Director


CREDIT SUISSE FIRST BOSTON                     CIBC INC.


By /s/ JUDITH E. SMITH                         By /s/ TEFTA GHILAGA
  --------------------------                     -------------------------------
 Title: Director                                 Title: Executive Director
                                                        CIBC Oppenheimer Corp.,
By /s/ TODD C. MORGAN                                   AS AGENT
  --------------------------
 Title: Director


FIRST UNION NATIONAL BANK                      BANK ONE (formerly, First 
                                                National Bank of Chicago)


By /s/ [SIGNATURE ILLEGIBLE]                   By /s/ SIGNATURE ILLEGIBLE]
  --------------------------                     -------------------------------
 Title:                                         Title: Corporate Banking Officer

                     Amendment No. 3 to Credit Agreement 
                     -----------------------------------
<PAGE>
 
                                      -7-

MELLON BANK, N.A.                                 ABN AMRO BANK N.V.


By /s/ [SIGNATURE ILLEGIBLE]                      By /s/ [SIGNATURE ILLEGIBLE]
  --------------------------                        ----------------------------
 Title: First Vice President                       Title: Senior Vice President

                                                  By /s/ WILLIAM S. BENNETT
                                                    ----------------------------
                                                   Title: Vice President


FLEET NATIONAL BANK                               DRESDNER BANK AG, NEW YORK
                                                   AND GRAND CAYMAN BRANCHES


By /s/ ADAM BESTER                                By /s/ CONSTANCE LOOSEMORE
  ---------------------------                       ----------------------------
 Title: Senior Vice President                      Title: Senior Vice President

                                                  By /s/ [SIGNATURE ILLEGIBLE]
                                                    ----------------------------
                                                   Title: Assistant Vice
                                                          President


PNC BANK, NATIONAL ASSOCIATION                    SUNTRUST BANK, CENTRAL
                                                   FLORIDA, N.A.


By /s/ JOHN T. WILDEN                             By /s/ DAVID D. MILLER
  ----------------------------                      ----------------------------
 Title: Vice President                             Title: Vice President

                      Amendment No. 3 to Credit Agreement
                      -----------------------------------
<PAGE>
 
                                      -8-

          By its signature below, the undersigned hereby consents to the
foregoing Amendment No. 3 and confirms that the obligations of the Borrower
under said Credit Agreement as amended by said Amendment No. 3 shall constitute
"Guaranteed Obligations" under the Guarantee and Pledge Agreement under and as
defined in said Credit Agreement for all purposes of said Guarantee and Pledge
Agreement.


                                        MEDIACOM LLC


                                        By: /s/ ROCCO B. COMMISSO
                                           ---------------------------------
                                           Rocco B. Commisso, as Manager


                      Amendment No. 3 to Credit Agreement
                      -----------------------------------
<PAGE>
 
                                                                      SCHEDULE 1
                                                              to Amendment No. 3


                          Revolving Credit Commitments
                          ----------------------------


<TABLE>
<CAPTION>
 
                                                                                              
Lender                                                        Revolving Credit Commitment
------                                                        ---------------------------
<S>                                                           <C>
The Chase Manhattan Bank                                      $ 27,000,000.00

Bank of Montreal                                              $ 24,000,000.00

Credit Suisse First Boston                                    $ 14,000,000.00

CIBC, Inc.                                                    $ 22,000,000.00

First Union National Bank                                     $ 20,222,222.22

The First National Bank of Chicago                            $ 20,000,000.00

Mellon Bank, N.A.                                             $ 20,000,000.00

ABN AMRO Bank N.V.                                            $ 19,777,777.78

Fleet National Bank                                           $ 18,000,000.00

Dresdner Bank AG, New York and Grand Cayman Branches          $ 15,000,000.00

PNC Bank, National Association                                $ 15,000,000.00

SunTrust Bank, Central Florida                                $ 10,000,000.00

TOTAL                                                         $225,000,000.00
</TABLE>

                      Amendment No. 3 to Credit Agreement
                      -----------------------------------
<PAGE>
 
                                      -1-

                                                                       EXHIBIT A


                  [Form of Opinion of Counsel to the Obligors]

                                        _______, 1999


To the Lenders party to Amendment
No. 3 to the Credit Agreement referred to
below and The Chase Manhattan
Bank, as Administrative Agent


Ladies and Gentlemen:

          We have acted as counsel to Mediacom Southeast LLC (the "Borrower"),
                                                                   --------
and Mediacom LLC ("Mediacom") in connection with (i) the Credit Agreement (the
                   --------
"Credit Agreement") dated as of January 23, 1998, between the Borrower, the
 ----------------
lenders party thereto and The Chase Manhattan Bank, as Administrative Agent,
providing for loans to be made by said lenders to the Borrower in an aggregate
principal amount not exceeding $225,000,000, (ii) Amendment No. 3 thereto dated
as of January 26, 1999 ("Amendment No. 3") and (iii) the various other
                         ---------------
agreements, instruments and other documents referred to in the next following
paragraph. Terms defined in Amendment No. 3 (including terms incorporated by
reference into Amendment No. 3) are used herein as defined therein; in addition,
the Credit Agreement as amended by Amendment No. 3 is referred to herein as the
"Amended Credit Agreement". This opinion letter is being delivered pursuant to
 ------------------------
Section 5(iii)(c) of Amendment No. 3.

          In rendering the opinions expressed below, we have examined the
following agreements, instruments and other documents:

          (a)      the Credit Agreement;

          (b)      Amendment No. 3;

          (c)      the New Notes being executed and delivered to the Lenders on
                   the date hereof (collectively, the "New Notes");
                                                       ---------

                       Opinion of Counsel to the Obligors
                       ----------------------------------
<PAGE>
 
                                      -2-

          (d)      the Confirmation and Consent of Mediacom appended to
                   Amendment No. 3 (the "Confirmation and Consent"); and
                                         ------------------------
          (e)      such records of the Borrower and such other documents as we
                   have deemed necessary as a basis for the opinions expressed
                   below.

Amendment No. 3, the Amended Credit Agreement, the New Notes and the
Confirmation and Consent are collectively referred to as the "Credit Documents";
                                                              ----------------  
the Borrower and Mediacom are herein collectively referred to as the "Relevant
                                                                      --------
Parties".
-------  

          We have also examined originals, or copies certified to our
satisfaction, of such corporate records, certificates of public officials of
pertinent states, certificates of corporate officers of the Relevant Parties and
such other instruments or documents as we have deemed necessary as a basis for
the opinions hereinafter set forth. As to questions of fact, we have, to the
extent that such facts were not independently established by us, relied upon
such certificates and we have assumed that any such certificates or other
evidence which was given or dated earlier than the date of this letter has
remained accurate, as far as relevant to the opinions contained herein, from
such earlier date through and including the date of this letter. In rendering
the opinions hereinafter set forth as to factual matters, we have also relied
upon, and assumed the accuracy of, the representations and warranties made in
the Credit Documents by the Relevant Parties. Whenever any statement herein is
qualified by our knowledge, it is intended to indicate that, during the course
of our representation of the Relevant Parties no information that would give us
actual knowledge of the inaccuracy of such statement has come to the attention
of the attorneys presently in this firm and who are actively engaged in the
representation of the Relevant Parties.

          In our examination, we have assumed the genuineness of all signatures,
the authenticity of all documents submitted to us as originals and the
conformity with authentic original documents of all documents submitted to us as
copies.

          In rendering the opinions expressed below, we have assumed, with
respect to all of the documents referred to in this opinion letter, that
(except, to the extent set forth in the opinions expressed below, as to the
Relevant Parties):

          (i)    such documents have been duly authorized by, have been duly
                 executed and delivered by, and constitute legal, valid, binding
                 and enforceable obligations of, all of the parties to such
                 documents;

          (ii)   all signatories to such documents have been duly authorized;
                 and

                      Opinion of Counsel to the Obligors
                      ----------------------------------
<PAGE>
 
                                      -3-

          (iii)  all of the parties to such documents are duly organized and
                 validly existing and have the power and authority (corporate,
                 limited liability company, partnership or other) to execute,
                 deliver and perform such documents.

          Based upon and subject to the foregoing and subject also to the
comments and qualifications set forth below, and having considered such
questions of law as we have deemed necessary as a basis for the opinions
expressed below, we are of the opinion that:

          1.   The Borrower is a limited liability company duly organized,
     validly existing and in good standing under the laws of the State of
     Delaware. Mediacom is a limited liability company duly organized, validly
     existing and in good standing under the laws of the State of New York.

          2.   Each Relevant Party has all requisite power to execute and
     deliver Amendment No. 3 and the New Notes, and to perform its obligations
     under, the Credit Documents to which it is a party. The Borrower has all
     requisite power to borrow under the Amended Credit Agreement.

          3.   The execution, delivery and performance by each Relevant Party of
     each Credit Document to which it is a party, and the borrowings by the
     Borrower under the Amended Credit Agreement, have been duly authorized by
     all necessary corporate or other action (as the case may be) on the part of
     such Relevant Party.

          4.   Amendment No. 3, the New Notes and the Confirmation and Consent
     have each been duly executed and delivered by each Relevant Party party
     thereto.

          5.   Each of the Credit Documents constitutes the legal, valid and
     binding obligation of each Relevant Party party thereto, enforceable
     against such Relevant Party in accordance with its terms, except as may be
     limited by bankruptcy, insolvency, reorganization, fraudulent conveyance,
     moratorium or other similar laws relating to or affecting the rights of
     creditors generally and except as the enforceability of the Credit
     Documents is subject to the application of general principles of equity
     (regardless of whether considered in a proceeding in equity or at law),
     including, without limitation, (a) the possible unavailability of specific
     performance, injunctive relief or any other equitable remedy and (b)
     concepts of materiality, reasonableness, good faith and fair dealing.

          6.   No authorization, approval or consent of, and no filing or
     registration with, any governmental or regulatory authority or agency of
     the United States of America or the State of New York is required on the
     part of any Relevant Party for the execution and 

                      Opinion of Counsel to the Obligors
                      ----------------------------------
<PAGE>
 
                                      -4-

     delivery of Amendment No. 3 or performance by any Relevant Party of the
     Amended Credit Agreement or for the borrowings by the Borrower under the
     Amended Credit Agreement.

          7.   The execution and delivery by each Relevant Party of Amendment
     No. 3, and the consummation by each Relevant Party of the transactions
     contemplated by the Amended Credit Agreement do not and will not (a)
     violate any provision of the limited liability company agreement, articles
     of organization, certificate of formation or the charter or by-laws or
     other organizational instrument of any Relevant Party, (b) violate any
     applicable law, rule or regulation, (c) violate any order, writ, injunction
     or decree of any court or governmental authority or agency or any arbitral
     award applicable to the Relevant Parties of which we have knowledge (after
     due inquiry) or (d) result in a breach of, constitute a default under,
     require any consent under, or result in the acceleration or required
     prepayment of any indebtedness pursuant to the terms of, any agreement or
     instrument of which we have knowledge to which any Relevant Party is a
     party or by which any of them is bound or to which any of them is subject,
     or (except for the Liens created pursuant to the Security Documents) result
     in the creation or imposition of any Lien upon any Property of any Relevant
     Party pursuant to, the terms of any such agreement or instrument.

          The foregoing opinions are subject to the following comments and
qualifications:

          (A)  The enforceability of Section 11.03 of the Amended Credit
     Agreement may be limited by (i) laws rendering unenforceable
     indemnification contrary to Federal or state securities laws and the public
     policy underlying such laws and (ii) laws limiting the enforceability of
     provisions exculpating or exempting a party, or requiring indemnification
     of a party for, liability for its own action or inaction, to the extent the
     action or inaction involves gross negligence, recklessness, willful
     misconduct or unlawful conduct.

          (B)  The enforceability of provisions in the Credit Documents to the
     effect that terms may not be waived or modified except in writing may be
     limited under certain circumstances.

          (C)  We express no opinion as to (i) the effect of the laws of any
     jurisdiction in which any Lender is located (other than the State of New
     York) that limit the interest, fees or other charges such Lender may
     impose, (ii) Section 4.07(c) of the Credit Agreement, (iii) the second
     sentence of Section 11.10 of the Credit Agreement (and any similar
     provisions in any of the other Credit Documents), insofar as such sentence
     relates to the subject matter jurisdiction of the United States District
     Court for the Southern District of New York to adjudicate any controversy
     related to any of the Credit Documents and (iv) the applicability to the
     obligations of the Subsidiary Guarantors (or 

                      Opinion of Counsel to the Obligors
                      ----------------------------------
<PAGE>
 
                                      -5-

     the enforceability of such obligations) of Section 548 of the Bankruptcy
     Code, Article 10 of the New York Debtor Creditor Law, or any provision of
     law relating to fraudulent conveyances, transfers or obligations.

          We express no opinion (a) as to the, and the effect of, compliance or
non-compliance by the Lenders or the Administrative Agent with any law, rule or
regulation applicable because of the legal or regulatory status or the specific
nature of the business of such Lender or Administrative Agent and (b) regarding
any law, rule or regulation to which any of the Relevant Parties may be subject,
or any approval which any of the Relevant Parties may be required to obtain,
because of the legal or regulatory status of the Lenders or the Administrative
Agent or because of any facts specifically pertaining to the Lenders or the
Administrative Agent.

          Our opinions are limited to the specific issues addressed and are
limited in all respects to laws and facts existing on the date hereof. By
rendering our opinions, we do not undertake to advise you of any changes in such
laws or facts which may occur after the date hereof.

          The foregoing opinions are limited to matters involving the Federal
laws of the United States, the Delaware General Corporation Law, the Delaware
Limited Liability Company Act and the law of the State of New York, and we do
not express any opinion as to the laws of any other jurisdiction (nor do we
express any opinion as to the applicability to, or the effect upon, the
transactions contemplated by the Credit Documents of the Federal Communications
Act of 1934, as amended, and the rules and regulations promulgated thereunder or
the policies of the FCC).

                      Opinion of Counsel to the Obligors
                      ----------------------------------
<PAGE>
 
                                      -6-

          At the request of our clients, this opinion letter is, pursuant to
Section 5(iii)(c) of Amendment No. 3, provided to you by us in our capacity as
counsel to the Relevant Parties and may not be relied upon by any Person for any
purpose other than in connection with the transactions contemplated by the
Amended Credit Agreement without, in each instance, our prior written consent.

                                        Very truly yours,



                                        [COOPERMAN LEVITT WINIKOFF
                                          LESTER & NEWMAN, P.C.]

                                        By:
                                           ------------------------

                      Opinion of Counsel to the Obligors
                      ----------------------------------
<PAGE>
 
                                      -1-

                                                                       EXHIBIT B



             [Form of Opinion of Special New York Counsel to Chase]

                                        _______, 1999


To the Lenders party to Amendment
No. 3 to the Credit Agreement referred to
below and The Chase Manhattan
Bank, as Administrative Agent

Ladies and Gentlemen:

          We have acted as special New York counsel to The Chase Manhattan Bank
                                                                       
("Chase") in connection with (i) the Credit Agreement dated as of January 23,
  -----                                                                      
1998 (the "Credit Agreement") between Mediacom Southeast LLC (the "Borrower"),
           ----------------                                        --------   
the lenders party thereto, Chase, as Administrative Agent, and First Union
National Bank, as Documentation Agent, providing for loans to be made by said
lenders to the Borrower in an aggregate principal amount not exceeding
$225,000,000, (ii) Amendment No. 3 thereto dated as of January 26, 1999 and (ii)
the various other agreements, instruments and other documents referred to in the
next following paragraph.  Terms defined in Amendment No. 3 (including terms
incorporated by reference into Amendment No. 3) are used herein as defined
therein; in addition, the Credit Agreement as amended by Amendment No. 3 is
referred to herein as the "Amended Credit Agreement".  This opinion letter is
                           ------------------------                          
being delivered pursuant to Section 5(iii)(d) of Amendment No. 3.

          In rendering the opinions expressed below, we have examined the
following agreements, instruments and other documents:

          (a)      the Credit Agreement;

          (b)      Amendment No. 3; and

          (c)      the New Notes being executed and delivered to the Lenders on
                   the date hereof (collectively, the "New Notes").
                                                       ---------

                          Opinion of Counsel to Chase
                          ---------------------------
<PAGE>
 
                                      -2-

Amendment No. 3, the Amended Credit Agreement, the New Notes and the
Confirmation and Consent are collectively referred to as the "Credit Documents";
                                                              ----------------  
the Borrower and Mediacom are herein collectively referred to as the "Relevant
                                                                      --------
Parties".
-------  

          In our examination, we have assumed the genuineness of all signatures,
the authenticity of all documents submitted to us as originals and the
conformity with authentic original documents of all documents submitted to us as
copies. When relevant facts were not independently established, we have relied
upon representations made in or pursuant to Amendment No. 3 and the Amended
Credit Agreement.

          In rendering the opinions expressed below, we have assumed, with
respect to all of the documents referred to in this opinion letter, that:

          (i)    such documents have been duly authorized by, have been duly
                 executed and delivered by, and (except to the extent set forth
                 in the opinions below as to the Borrower) constitute legal,
                 valid, binding and enforceable obligations of, all of the
                 parties to such documents;

          (ii)   all signatories to such documents have been duly authorized;
                 and

          (iii)  all of the parties to such documents are duly organized and
                 validly existing and have the power and authority (corporate or
                 other) to execute, deliver and perform such documents.

          Based upon and subject to the foregoing and subject also to the
comments and qualifications set forth below, and having considered such
questions of law as we have deemed necessary as a basis for the opinions
expressed below, we are of the opinion that each of Amendment No. 3 and the
Amended Credit Agreement constitutes the legal, valid and binding obligation of
each Relevant Party party thereto, enforceable against such Relevant Party in
accordance with its terms, except as may be limited by bankruptcy, insolvency,
reorganization, moratorium or other similar laws relating to or affecting the
rights of creditors generally and except as the enforceability of Amendment No.
3 or the Amended Credit Agreement is subject to the application of general
principles of equity (regardless of whether considered in a proceeding in equity
or at law), including, without limitation, (a) the possible unavailability of
specific performance, injunctive relief or any other equitable remedy and (b)
concepts of materiality, reasonableness, good faith and fair dealing.

          The foregoing opinions are subject to the following comments and
qualifications:

          (A)  The enforceability of Section 11.03 of the Amended Credit
     Agreement may be limited by (i) laws rendering unenforceable
     indemnification contrary to Federal or state securities laws and the public
     policy underlying such laws and (ii) laws limiting the 

                          Opinion of Counsel to Chase
                          ---------------------------
<PAGE>
 
                                      -3-

     enforceability of provisions exculpating or exempting a party, or requiring
     indemnification of a party for, liability for its own action or inaction,
     to the extent the action or inaction involves gross negligence,
     recklessness, willful misconduct or unlawful conduct.

          (B)  The enforceability of provisions in the Credit Documents to the
     effect that terms may not be waived or modified except in writing may be
     limited under certain circumstances.

          (C)  We express no opinion as to (i) the effect of the laws of any
     jurisdiction in which any Lender is located (other than the State of New
     York) that limit the interest, fees or other charges such Lender may
     impose, (ii) Section 4.07(c) of the Amended Credit Agreement, and (iii) the
     second sentence of Section 11.10 of the Amended Credit Agreement, insofar
     as such sentence relates to the subject matter jurisdiction of the United
     States District Court for the Southern District of New York to adjudicate
     any controversy related to the Credit Documents and (iv) the applicability
     to the obligations of the Subsidiary Guarantors (or the enforceability of
     such obligations) of Section 548 of the Bankruptcy Code, Article 10 of the
     New York Debtor Creditor Law, or any provision of law relating to
     fraudulent conveyances, transfers or obligations.

          The foregoing opinions are limited to matters involving the Federal
laws of the United States and the law of the State of New York, and we do not
express any opinion as to the laws of any other jurisdiction (nor do we express
any opinion as to the applicability to, or the effect upon, the transactions
contemplated by the Credit Documents of the Federal Communications Act of 1934,
as amended, the rules and regulations promulgated thereunder or the policies of
the FCC).

          At the request of our client, this opinion letter is, pursuant to
Section 5(iii)(d) of Amendment No. 3, provided to you by us in our capacity as
special New York counsel to Chase and may not be relied upon by any Person for
any purpose other than in connection with the transactions contemplated by the
Amended Credit Agreement without, in each instance, our prior written consent.

                                        Very truly yours,


RJW/___

                          Opinion of Counsel to Chase
                          ---------------------------