Document:

<PAGE>

                                                                     EXHIBIT 4.1

                       AMENDMENT NO. 1 TO CREDIT AGREEMENT

     Amendment No. 1 (this "Amendment"), dated as of June 27, 2002, among Terra
Capital, Inc., a Delaware corporation ("Terra Capital"), Terra Nitrogen (U.K.),
Limited, a company incorporated in England and Wales ("Terra UK"), and Terra
Nitrogen, Limited Partnership, a Delaware limited partnership ("TNLP") (Terra
Capital, Terra UK and TNLP each a "Borrower" and, collectively, the
"Borrowers"), Terra Industries Inc., a Maryland corporation ("Terra
Industries"), and the Lenders party hereto, amends certain provisions of the
Amended and Restated Credit Agreement, dated as of October 10, 2001 (as amended
hereby and as the same may be further amended, supplemented or otherwise
modified from time to time, the "Credit Agreement"), among the Borrowers, Terra
Industries, the financial institutions from time to time party thereto as
lenders (the "Lenders"), the financial institutions from time to time party
thereto as issuing banks (the "Issuers") and Citicorp USA, Inc. ("CUSA"), as
agent for the Lenders and the Issuers (in such capacity, the "Administrative
Agent").

                              W I T N E S S E T H:

     WHEREAS, pursuant to the Credit Agreement, the Lenders have agreed to make
Loans to the Borrowers and to issue, and have issued, Letters of Credit for the
account of the Borrowers; and

     WHEREAS, the Borrowers, Terra Industries, the Requisite Lenders and the
Administrative Agent have agreed to certain amendments to the Credit Agreement
as more specifically set forth below;

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
and provisions hereinafter contained, the parties hereto hereby agree as
follows:

     1.   Defined Terms. Capitalized terms used herein and not defined herein
          but defined in the Credit Agreement are used herein as defined in the
          Credit Agreement.

     2.   Amendments to the Credit Agreement. As of the Amendment Effective Date
          (as defined in Section 3 below), the Credit Agreement is hereby
          amended as follows:

          (a)  Amendment to Section 5.1. Section 5.1 of the Credit Agreement is
               hereby amended and restated in its entirety to read as follows:

          Section 5.1 Minimum Cash Flow. If, at any time during any Fiscal
     Quarter, the aggregate Available Credit is less than $60,000,000 for more
     than three consecutive Business Days, Terra Industries will have Cash Flow
     for the four Fiscal Quarter period set forth below ending as of the last
     day of the immediately preceding Fiscal Quarter of not less than the amount
     set forth below opposite such period:

<PAGE>

----------------------------------------------------- --------------------------
                  Fiscal Quarters                          Minimum Cash Flow
----------------------------------------------------- --------------------------
4 Fiscal Quarters ended September 30, 2001,
December 31, 2001 and March 31, 2002                         $40,000,000
----------------------------------------------------- --------------------------
4 Fiscal Quarters ended June 30, 2002                        $45,000,000
----------------------------------------------------- --------------------------
4 Fiscal Quarters ended September 30, 2002                   $50,000,000
----------------------------------------------------- --------------------------
4 Fiscal Quarters ended December 31, 2002 and each
4 Fiscal Quarter period thereafter                           $60,000,000
----------------------------------------------------- --------------------------

         For avoidance of doubt, an Event of Default for purposes of Section
         9.1(e)(i) in respect of the minimum Cash Flow requirement indicated
         above shall be deemed to have occurred and be continuing as of the next
         Business Day immediately following the aforementioned three consecutive
         Business Days in the event that Terra Industries shall not have met the
         Cash Flow requirement set forth above.

     3. Conditions Precedent to the Effectiveness of this Amendment. This
Amendment shall become effective as of the date hereof on the date (the
"Amendment Effective Date") when the following conditions precedent have been
satisfied:

          (a) Certain Documents. The Administrative Agent shall have received,
     on or before the Amendment Effective Date, all of the following, all of
     which shall be in form and substance satisfactory to the Administrative
     Agent, in sufficient originally executed copies for each of the Lenders:

               (i) this Amendment, executed by each Borrower, Terra Industries,
          and the Lenders constituting the Requisite Lenders; and

               (ii) such additional documentation as the Administrative Agent or
          the Requisite Lenders may reasonably require.

          (b) Representations and Warranties. Each of the representations and
     warranties made by the Borrowers or Terra Industries in or pursuant to the
     Credit Agreement, as amended hereby, and the other Loan Documents to which
     the Borrowers or Terra Industries is a party or by which the Borrowers or
     Terra Industries is bound, shall be true and correct in all material
     respects on and as of the Amendment Effective Date (other than
     representations and warranties in any such Loan Document which expressly
     speak as of a specific date, which shall have been true and correct in all
     material respects as of such specific date).

          (c) No Event of Default. No Default of Event of Default shall have
     occurred and be continuing on the Amendment Effective Date.

          (d) Fees and Past Expenses Paid. On the Amendment Effective Date the
     Borrowers shall have paid (i) to each Lender that has executed this
     Amendment an

                                        2

<PAGE>

amendment fee equal to 0.125 percent (0.125%) of such Lender's Revolving
Credit Commitments and any other fees required to be paid herewith under any
Loan Documents and, (ii) in accordance with Section 11.3 of the Credit
Agreement, all outstanding costs and expenses of the Administrative Agent
previously billed to the Borrowers, including the reasonable fees and
out-of-pocket expenses of counsel for the Administrative Agent.

     4. Representations and Warranties. On and as of the date hereof, and as of
the Amendment Effective Date, after giving effect to this Amendment, each
Borrower and Terra Industries hereby represents and warrants to the Lenders as
follows:

          (a) Each of the representations and warranties contained in Article IV
     of the Credit Agreement, the other Loan Documents or in any certificate,
     document or financial or other statement furnished at any time under or in
     connection therewith are true and correct in all material respects on and
     as of the date as if made on and as of such date, except to the extent that
     such representations and warranties specifically relate to a specific date,
     in which case such representations and warranties shall be true and correct
     in all material respects as of such specific date; provided, however, that
     references therein to the "Credit Agreement" shall be deemed to include
     this Amendment;

          (b) No Default or Event of Default has occurred and is continuing.

     5. Continuing Effect; No Other Amendments. Except as expressly amended
hereby, all of the terms and provisions of the Credit Agreement and the other
Loan Documents are and shall remain in full force and effect. The amendments and
consents contained herein shall not constitute an amendment or a waiver of any
other provision of the Credit Agreement or the other Loan Documents or for any
other purpose except as expressly set forth herein.

     6. Costs and Expenses. The Borrowers and Terra Industries agree to pay on
demand all reasonable and documented out-of-pocket costs and expenses of the
Administrative Agent in connection with the preparation, execution and delivery
of this Amendment and other instruments and documents to be delivered pursuant
hereto, including the reasonable and documented fees and out-of-pocket expenses
of counsel for the Administrative Agent with respect thereto.

     7. Governing Law; Counterparts; Miscellaneous.

          (a) This Amendment shall be governed by, and construed and interpreted
     in accordance with, the law of the State of New York.

          (b) This Amendment may be executed in any number of counterparts and
     by the different parties on separate counterparts, each of which
     counterparts when executed and delivered shall be an original, but all of
     which shall together constitute one and the same instrument.

          (c) Section captions used in this Amendment are for convenience only
     and shall not affect the construction of this Amendment.

          (d) From and after the Amendment Effective Date, all references in the
     Credit Agreement to the "Agreement" shall be deemed to be references to
     such Agreement as

                                        3

<PAGE>

     modified hereby and this Amendment and the Credit Agreement shall be read
     together and construed as a single instrument.

                            [Signature Pages Follow]

                                        4

<PAGE>

     IN WITNESS WHEREOF, the undersigned parties have executed this AMENDMENT
NO. 1 TO CREDIT AGREEMENT to be effective for all purposes as of the Amendment
Effective Date.

                                       Borrowers
                                       ---------

                                       Terra Capital, Inc.

                                       By: /s/ F. G. Meyer
                                           -------------------------------------
                                           Name:  F. G. Meyer
                                           Title: Vice President

                                       Terra Nitrogen (U.K.), Limited

                                       By: /s/ F. G. Meyer
                                           -------------------------------------
                                           Name:  F. G. Meyer
                                           Title: Director

                                       Terra Nitrogen, Limited Partnership

                                       By: Terra Nitrogen Corporation,
                                           its General Partner

                                       By: /s/ F. G. Meyer
                                           -------------------------------------
                                           Name:  F. G. Meyer
                                           Title: Vice President

                                       Guarantor
                                       ---------

                                       Terra Industries Inc.

                                       By: /s/ F. G. Meyer
                                           -------------------------------------
                                           Name:  F. G. Meyer
                                           Title: Senior Vice President and
                                           Chief Financial Officer

                                       Lenders
                                       -------

                                       Citicorp USA, Inc.

                                       By: /s/ David Jaffe
                                           -------------------------------------
                                           Name:  David Jaffe
                                           Title: Vice President

                      Signature Page to Amendment No. 1 to
                                Credit Agreement

<PAGE>

                                       Foothill Capital Corporation

                                       By: /s/ Mike Baranowski
                                           -------------------------------------
                                           Name:  Mike Baranowski
                                           Title: Vice President

                                       LaSalle Bank National Association

                                       By: /s/ Mitchell Tarvid
                                           -------------------------------------
                                           Name:  Mitchell Tarvid
                                           Title: Vice President

                                       PNC Business Credit

                                       By: /s/ Manuel R. Borges
                                           -------------------------------------
                                           Name:  Manuel R. Borges
                                           Title: Assistant Vice President

                                       Congress Financial Corp.

                                       By: /s/ Thomas A. Martin
                                           -------------------------------------
                                           Name:  Thomas A. Martin
                                           Title: Vice President

                                       Heller Financial, Inc.

                                        By: /s/ W. Jerome McDermott
                                            ------------------------------------
                                            Name:  W. Jerome McDermott
                                            Title: Duly Authorized Signatory

                                        The Provident Bank

                                        By: /s/ Marshall M. Stuart
                                            ------------------------------------
                                            Name:  Marshall M. Stuart
                                            Title: Vice President

                      Signature Page to Amendment No. 1 to
                                Credit Agreement<PAGE>
                                                                  EXHIBIT 4.1(a)

                          [SPECIMEN STOCK CERTIFICATE]

      NUMBER

CA

INCORPORATED UNDER THE LAWS          CLASS A                 SHARES
 OF THE STATE OF DELAWARE         COMMON STOCK

                                PAR VALUE ($0.001)

                                [CINEMARK LOGO]

THIS CERTIFICATE TRANSFERABLE IN                  CUSIP 17243R 10 1
   NEW YORK CITY, NEW YORK            SEE REVERSE FOR CERTAIN DEFINITIONS AND
                                      INFORMATION REGARDING THE CERTIFICATE OF
                                              INCORPORATION AS AMENDED

THIS CERTIFIES THAT

IS THE OWNER OF

             FULLY-PAID AND NON-ASSESSABLE SHARES OF CLASS A COMMON STOCK OF
CINEMARK, INC. transferable on the books of the Corporation by the holder hereof
in person or by duly authorized attorney upon surrender of this Certificate
properly endorsed. This Certificate is not valid unless countersigned by the
Transfer Agent and registered by the Registrar.

     Witness the facsimile seal of the Corporation and the facsimile signatures
of its authorized officers.

                                                   Dated:

          CHAIRMAN                                 COUNTERSIGNED AND REGISTERED:
    [Facsimile Signature]

                                                               TRANSFER AGENT
                                                               AND REGISTRAR,

          SECRETARY                                By: The Bank of New York
    [Facsimile Signature]                                  AUTHORIZED SIGNATURE

<PAGE>

                                 CINEMARK, INC.

THIS CERTIFICATE AND THE SHARES REPRESENTED HEREBY ARE ISSUED UNDER AND SHALL BE
SUBJECT TO ALL OF THE PROVISIONS OF THE CERTIFICATE OF INCORPORATION, AS
AMENDED, OF THE CORPORATION. THE CORPORATION WILL FURNISH TO THE RECORD HOLDER
OF THIS CERTIFICATE WITHOUT CHARGE ON WRITTEN REQUEST TO THE CORPORATION AT ITS
PRINCIPAL PLACE OF BUSINESS OR REGISTERED OFFICE A DESCRIPTION OF THE AUTHORIZED
COMMON STOCK AND PREFERRED STOCK OF THE CORPORATION AND A STATEMENT OF THE
POWERS, DESIGNATIONS, PREFERENCES, AND RELATIVE PARTICIPATING, OPTIONAL OR OTHER
SPECIAL RIGHTS OF SUCH STOCK AND THE QUALIFICATIONS, LIMITATIONS, OR
RESTRICTIONS OF SUCH PREFERENCES OR RIGHTS.

     The following abbreviations, when used in the inscription on the face of
this certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

<Table>
<S>           <C>                                   <C>
     TEN COM  - as tenants in common                UNIF GIFT MIN ACT -_______Custodian ____________
     TEN ENT  - as tenants by the entireties                            (Cust)               (Minor)
     JT TEN   - as joint tenants with right                            Under Uniform Gifts to Minors
                of survivorship and not as                             Act _________________________
                tenants in common                                                   (State)
</Table>

                      Additional abbreviations may also be used though not in
the above list.

     For Value Received, ___________________ hereby sell(s), assign(s) and
transfer(s) unto

PLEASE INSERT SOCIAL SECURITY OR OTHER
IDENTIFYING NUMBER OF ASSIGNEE

________________________________________________________________________________

________________________________________________________________________________
                  (PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS,
                   INCLUDING ZIP OR POSTAL CODE, OF ASSIGNEE)
________________________________________________________________________________

________________________________________________________________________________

______________________________________________________________________ Shares of
the Class A Common Stock represented by the within certificate, and do hereby
irrevocably constitute and appoint _________________________________ Attorney to
transfer the said shares on the books of the within named Corporation with full
power of substitution in the premises.

Dated
      -----------------

                  NOTICE:

        THE SIGNATURE(S) TO THIS       X
        ASSIGNMENT MUST CORRESPOND      ----------------------------------------
        WITH THE NAME(S) AS WRITTEN                  (SIGNATURE)
        UPON THE FACE OF THE
        CERTIFICATE IN EVERY           X
        PARTICULAR WITHOUT ALTERATION   ----------------------------------------
        OR ENLARGEMENT OR ANY CHANGE                 (SIGNATURE)
        WHATEVER.

                                        ----------------------------------------
                                        THE SIGNATURE(S) SHOULD BE GUARANTEED BY
                                        AN ELIGIBLE GUARANTOR INSTITUTION
                                        (BANKS, STOCKBROKERS, SAVINGS AND LOAN
                                        ASSOCIATIONS AND CREDIT UNIONS WITH
                                        MEMBERSHIP IN AN APPROVED SIGNATURE
                                        GUARANTEE MEDALLION PROGRAM), PURSUANT
                                        TO S E C RULE 17Ad-15.
                                        ----------------------------------------
                                        SIGNATURE(S) GUARANTEED BY:

                                        ----------------------------------------

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