<PAGE>
 
                                                                    EXHIBIT 4.48

                                                                       EXECUTION



                        GRANITE BROADCASTING CORPORATION

                                 THIRD AMENDMENT
                 TO THIRD AMENDED AND RESTATED CREDIT AGREEMENT

     This THIRD AMENDMENT TO THIRD AMENDED AND RESTATED CREDIT AGREEMENT (this
"Amendment") is dated as of April 16, 1998 and entered into by and among Granite
Broadcasting Corporation, a Delaware corporation ("Company"), the Guarantors
listed on the signature pages hereof (the "Guarantors"), the financial
institutions listed on the signature pages hereof ("Lenders"), Bankers Trust
Company, as agent for Lenders (in such capacity , "Agent"), and The Bank of New
York, First Union National Bank of North Carolina, Goldman Sachs Credit Partners
L.P. and Union Bank of California, N.A., as co-agents (in such capacity,
"Co-Agents"), and is made with reference to that certain Third Amended and
Restated Credit Agreement dated as of September 4, 1996, as amended by that
certain First Amendment to Third Amended and Restated Credit Agreement dated as
of June 6, 1997 and that certain Second Amendment to Third Amended and Restated
Credit Agreement dated as of February 17, 1998 (as so amended, the "Credit
Agreement"), by and among Company, Lenders, Agent and Co-Agents. Capitalized
terms used herein without definition shall have the same meanings herein as set
forth in the Credit Agreement.

                                    RECITALS

     WHEREAS, Company and Lenders desire to amend the Credit Agreement to make
certain amendments as set forth below.

     NOW, THEREFORE, in consideration of the premises and the agreements,
provisions and covenants herein contained, and pursuant to subsection 10.6 of
the Credit Agreement, the parties hereto agree as follows:

     SECTION 1. AMENDMENTS TO THE CREDIT AGREEMENT

     Amendments to Section 7: Negative Covenants

     Section 7 of the Credit Agreement is hereby amended by amending and
restating subsection 7.1(xi) thereof in its entirety as follows:

          "(xi) so long as at the time of incurrence thereof no Event of Default
     or Potential Event of Default has occurred and is continuing or would be
     caused thereby, Company may from time to time following the Closing Date
     issue debt Securities subordinate in right and time of payment to the
     Obligations (the "Additional Subordinated Indebtedness"); provided that (a)
     such Additional Subordinated Indebtedness is unsecured, (b) the maturity of
     such Additional Subordinated Indebtedness is no earlier than December 31,
     2003, (c) such Additional Subordinated Indebtedness includes
     representations and warranties, covenants, events of default and other
     provisions that are not more restrictive or burdensome to Company than any
     other Subordinated Indebtedness, (d) the subordination provisions of such
     Additional Subordinated Indebtedness are no less favorable to the Lenders
     than the subordination provisions of any other Subordinated Indebtedness,
     (e) the mandatory 
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     redemption, retirement, sinking fund or payment provisions of such
     Additional Subordinated Indebtedness do not require redemption, repurchase
     or payment of any amount in any circumstances which any other Subordinated
     Indebtedness would not require redemption, repurchase or similar payment of
     any amount, (f) Company can demonstrate in form and substance satisfactory
     to Agent that, immediately after giving effect to such Additional
     Subordinated Indebtedness, Company is in compliance on a Pro Forma Basis
     with all covenants set forth in Section 6 and 7 of this Agreement through
     the Revolving Loan Commitment Termination Date, and (g) Company applies the
     Net Debt Proceeds of such Additional Subordinated Indebtedness to prepay
     the Loans and reduce the Commitments pursuant to subsection 2.4B(iii)(c) to
     the extent required thereby."

     SECTION 2. CONDITIONS TO EFFECTIVENESS

     This Amendment shall become effective (the "Third Amendment Effective
Date") only upon receipt by Agent of counterparts hereof duly executed by
Company, Guarantors and Requisite Lenders or, in the case of any Lender,
telecopy or telephone confirmation from such Lender of its execution hereof.

     SECTION 3. COMPANY'S REPRESENTATIONS AND WARRANTIES

     In order to induce Requisite Lenders to enter into this Amendment and to
amend the Credit Agreement in the manner provided herein, Company represents and
warrants to each Lender that the following statements are true, correct and
complete:

          A. Authorization; Binding Obligations. Company has all requisite
     corporate power and authority to enter into this Amendment. The execution,
     delivery and performance of this Amendment have been duly authorized by all
     necessary corporate action by Company. This Amendment has been duly
     executed and delivered by Company and is the legally valid and binding
     obligation of Company, enforceable against Company in accordance with its
     terms, except as enforceability may be limited by bankruptcy, insolvency,
     reorganization, moratorium or similar laws relating to or limiting
     creditors' rights generally and by equitable principles relating to
     enforceability.

          B. No Conflict. The execution and delivery by Company of this
     Amendment do not and will not (i) violate any provision of any law or any
     governmental rule or regulation applicable to Company or any of its
     Subsidiaries, the Certificate or Articles of Incorporation or Bylaws of
     Company or any of its Subsidiaries or any order, judgment or decree of any
     court or other agency of government binding on Company or any of its
     Subsidiaries, (ii) conflict with, result in a breach of or constitute (with
     due notice or lapse of time or both) a default under any Contractual
     Obligation of Company or any of its Subsidiaries, (iii) result in or
     require the creation or imposition of any Lien upon any of the properties
     or assets of Company or any of its Subsidiaries (other than any Liens
     created under any of the Loan Documents in favor of Agent on behalf of
     Lenders), or (iv) require any approval of stockholders or any approval or
     consent of any Person under any Contractual Obligation of Company or any of
     its Subsidiaries.

          C. Governmental Consents. The execution and delivery by Company of
     this Amendment do not and will not require any registration with, consent
     or approval of, or notice to, or other action to, with or by, any federal,
     state or other governmental authority or regulatory body, except to the
     extent that Company is required to file this Amendment with the FCC.

          D. Incorporation of Representations. Each representation and warranty
     of Company contained in each of the Loan Documents is true, correct and
     complete in all material 


                                       2
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     respects on and as of the Third Amendment Effective Date to the same extent
     as though made on and as of the Third Amendment Effective Date except to
     the extent such representations and warranties relate to an earlier date,
     in which case they were true, correct and complete in all material respects
     as of such earlier date.

          E. Absence of Default. No event has occurred and is continuing or
     would result from the execution, delivery or performance of this Amendment
     that constitutes or would constitute an Event of Default or a Potential
     Event of Default after giving effect to this Amendment.

     SECTION 4. ACKNOWLEDGEMENT AND CONSENT

     Each Guarantor hereby acknowledges that it has read this Amendment and
consents to the terms thereof and further hereby confirms and agrees that,
notwithstanding the effectiveness of this Amendment, the obligations of such
Guarantor under the Subsidiary Guaranty shall not be impaired or affected and
the Subsidiary Guaranty is, and shall continue to be, in full force and effect
and is hereby confirmed and ratified in all respects.

     SECTION 5. MISCELLANEOUS

     A. Reference to and Effect on the Credit Agreement and the Other Loan
Documents.

          (i) On and after the Third Amendment Effective Date, each reference in
     the Credit Agreement to "this Agreement", "hereunder", "hereof", "herein"
     or words of like import referring to the Credit Agreement, and each
     reference in the other Loan Documents to the "Credit Agreement",
     "thereunder", "thereof" or words of like import referring to the Credit
     Agreement shall mean and be a reference to the Credit Agreement, as amended
     by this Amendment.

          (ii) Except as specifically amended by this Amendment, the Credit
     Agreement and the other Loan Documents shall remain in full force and
     effect and are hereby ratified and confirmed.

          (iii) The execution, delivery and performance of this Amendment shall
     not, except as expressly provided herein, constitute a waiver of any
     provision of, or operate as a waiver of any right, power or remedy of Agent
     or any Lender under, the Credit Agreement or any of the other Loan
     Documents.

     B. Fees and Expenses. Company acknowledges that all costs, fees and
expenses as described in subsection 10.2 of the Credit Agreement incurred by
Agent and its counsel with respect to this Amendment and the documents and
transactions contemplated hereby shall be for the account of Company.

     C. Headings. Section and subsection headings in this Amendment are included
herein for convenience of reference only and shall not constitute a part of this
Amendment for any other purpose or be given any substantive effect.

     D. Applicable Law. THIS AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF THE
PARTIES HEREUNDER SHALL BE GOVERNED BY, AND SHALL BE CONSTRUED AND ENFORCED IN
ACCORDANCE WITH, THE INTERNAL LAWS OF THE STATE OF NEW YORK (INCLUDING WITHOUT
LIMITATION SECTION 5-1401 OF THE GENERAL OBLIGATIONS LAW OF 


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THE STATE OF NEW YORK), WITHOUT REGARD TO CONFLICTS OF LAWS PRINCIPLES.

     E. Counterparts. This Amendment may be executed in any number of
counterparts and by different parties hereto in separate counterparts, each of
which when so executed and delivered shall be deemed an original, but all such
counterparts together shall constitute but one and the same instrument;
signature pages may be detached from multiple separate counterparts and attached
to a single counterpart so that all signature pages are physically attached to
the same document.


                  [Remainder of page intentionally left blank]

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed and delivered by their respective officers thereunto duly
authorized as of the date first written above.



           COMPANY:                       GRANITE BROADCASTING CORPORATION


                                             By: /s/ ELLEN MC CLAIN
                                                --------------------------------
                                                 Ellen McClain
                                                 Vice President




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     SUBSIDIARIES:     GRANITE RESPONSE TELEVISION, INC.
                       KBVO, INC.
                       KBVO LICENSE, INC.
                       KNTV, INC.
                       KNTV LICENSE, INC.
                       RJR COMMUNICATIONS, INC.
                       KBJR LICENSE, INC.
                       SAN JOAQUIN COMMUNICATIONS
                         CORPORATION
                       KSEE LICENSE, INC.,
                       WPTA-TV, INC.
                       WPTA-TV LICENSE, INC.
                       WTVH, INC.
                       WTVH LICENSE, INC.
                       WWMT-TV, INC.
                       WWMT-TV LICENSE, INC.
                       WKBW-TV, INC.
                       WKBW-TV LICENSE, INC.
                       QUEEN CITY BROADCASTING, INC.
                       QUEEN CITY BROADCASTING
                       OF NEW YORK, INC.
                       WXON, INC.
                       WXON LICENSE, INC.

                             By: /s/ ELLEN MC CLAIN
                                 ----------------------
                                     Ellen McClain


                             QUEEN CITY III LIMITED PARTNERSHIP
                             By: WKBW-TV, INC.,
                                 its General Partner


                                 By: /s/ ELLEN MCCLAIN
                                    ---------------------
                                     Ellen McClain



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     LENDERS:

                             BANKERS TRUST COMPANY,
                             individually and as Agent

                             By: /s/ PATRICIA HOGAN
                                 --------------------------------
                                 Name: Patricia Hogan
                                 Title: Principal

                             GOLDMAN SACHS CREDIT PARTNERS L.P.,
                             as a Co-Agent and a Lender

                             By: /s/ STEPHEN B. KING
                                 --------------------------------
                                 Name:  Stephen B. King
                                 Title:  Authorized Signatory

                             FIRST UNION NATIONAL BANK OF NORTH
                             CAROLINA,
                             as a Co-Agent and a Lender

                             By: /s/ BREE LOFTIN
                                 --------------------------------
                                 Name: Bree Loftin
                                 Title: Senior Vice President



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                             THE BANK OF NEW YORK,
                             as a Co-Agent and a Lender


                             By: /s/ BRIAN C. WASHINGTON
                                 -----------------------------------
                                 Name: Brian C. Washington
                                 Title: Assistant Vice President


                             UNION BANK OF CALIFORNIA, N.A.,
                             as a Co-Agent and a Lender

                             By: /s/ KRISTINA MOUZARIS
                                 -----------------------------------
                                 Name:  Kristina Mouzaris
                                 Title:  Assistant Vice President


                             THE BANK OF TOKYO-MITSUBISHI TRUST
                             COMPANY,
                             as a Lender


                             By: /s/ GLEN B. ECKERT
                                 -----------------------------------
                                 Name:  Glenn B. Eckert
                                 Title:  Vice President


                             NATEXIS BANQUE
                             as a Lender


                             By: /s/ FRANK H. MADDEN
                                 -----------------------------------
                                 Name:  Frank H. Madden
                                 Title: Vice President

                             By: /s/ WILLIAM C. MAIER
                                 -----------------------------------
                                 Name:  William C. Maier
                                 Title:  Vice President-Group Manager



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                             THE SUMITOMO BANK, LIMITED,
                             as a Lender


                             By: /s/ J.R. BREADLEY
                                 -----------------------------------
                                 Name: J.R. Breadley
                                 Title:  Vice President New York Office

                             By: /s/ BRIAN M. SMITH
                                 -----------------------------------
                                 Name: Brian M. Smith
                                 Title: Senior Vice Presidnt & Regional Manager


                             DRESDNER BANK AG, NEW YORK AND GRAND
                             CAYMAN BRANCHES,
                             as a Lender

                             By: /s/ WILLIAM E. LAMBERT
                                 -----------------------------------
                                 Name:  William E. Lambert
                                 Title:  Assistant Vice President

                             By: /s/ JANE A. MAJESKI
                                 -----------------------------------
                                 Name:  Jane A. Majeski
                                 Title:  First Vice President


                             ABN AMRO BANK N.V., NEW YORK BRANCH,
                             as a Lender


                             By: /s/ ANN SCHWALBENBERG
                                 -----------------------------------
                                 Name:  Ann Schwalbenberg
                                 Title:  Vice President


                             By: /s/ THOMAS T. ROGERS
                                 -----------------------------------
                                 Name:  Thomas T. Rogers
                                 Title:  Vice President



                                       8
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                             HELLER FINANCIAL, INC.,
                             as a Lender

                             By: /s/ PATRICK HAYES
                                 -----------------------------------
                                 Name: Patrick Hayes
                                 Title:  Vice President


                             MICHIGAN NATIONAL BANK,
                             as a Lender


                             By: /s/ STEPHANE LUBILA
                                 -----------------------------------
                                 Name: Stephane Lubila
                                 Title: Relationship Manager


                             BANQUE PARIBAS,
                             as a Lender


                             By: /s/ WILLIAM B. SCHINK
                                 -----------------------------------
                                 Name:  William B. Schink
                                 Title: Director


                             By: /s/ ERROL R. ANTZIS
                                 -----------------------------------
                                 Name: Errol R. Antzis
                                 Title: Managing Director, Group Head


                             THE BANK OF NOVA SCOTIA,
                             as a Lender


                             By: /s/ MARGOT C. BRIGHT
                                 -----------------------------------
                                 Name: Margot C. Bright
                                 Title: Authorized Signatory


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                             BANQUE NATIONALE DE PARIS,
                             as a Lender

                             By: /s/ SERGE DESRAYAUD
                                 -----------------------------------
                                 Name: Serge Desrayaud
                                 Title: Vice President


                             By: /s/ STEPHANIE R. ROGERS
                                 -----------------------------------
                                 Name: Stephanie R. Rogers
                                 Title: Vice President


                             COMPAGNIE FINANCIERE DE CIC ET DE
                             L'UNION EUROPEENNE,
                             as a Lender


                             By: /s/ MARCUS EDWARD
                                 -----------------------------------
                                 Name: Marcus Edward
                                 Title:  Vice President


                             By: /s/ ANTHONY ROCK
                                 -----------------------------------
                                 Name: Anthony Rock
                                 Title: Vice President