<PAGE>   1
                                                                  EXHIBIT 4.34



                    EIGHTEENTH AMENDMENT TO CREDIT AGREEMENT


         THIS EIGHTEENTH AMENDMENT TO CREDIT AGREEMENT (this "Amendment"), dated
as of February 11, 2000, is by and between KAISER ALUMINUM & CHEMICAL
CORPORATION, a Delaware corporation (the "Company"), KAISER ALUMINUM
CORPORATION, a Delaware corporation (the "Parent Guarantor"), the various
financial institutions that are or may from time to time become parties to the
Credit Agreement referred to below (collectively, the "Lenders" and,
individually, a "Lender"), and Bank of America, N.A. (successor to BankAmerica
Business Credit, Inc., a Delaware corporation), as agent (in such capacity,
together with its successors and assigns in such capacity, the "Agent") for the
Lenders. Capitalized terms used, but not defined, herein shall have the meanings
given to such terms in the Credit Agreement, as amended hereby.

                              W I T N E S S E T H:

         WHEREAS, the Company, the Parent Guarantor, the Lenders and the Agent
are parties to the Credit Agreement, dated as of February 15, 1994, as amended
by the First Amendment to Credit Agreement, dated as of July 21, 1994, the
Second Amendment to Credit Agreement, dated as of March 10, 1995, the Third
Amendment to Credit Agreement and Acknowledgement, dated as of July 20, 1995,
the Fourth Amendment to Credit Agreement, dated as of October 17, 1995, the
Fifth Amendment to Credit Agreement, dated as of December 11, 1995, the Sixth
Amendment to Credit Agreement, dated as of October 1, 1996, the Seventh
Amendment to Credit Agreement, dated as of December 17, 1996, the Eighth
Amendment to Credit Agreement, dated as of February 24, 1997, the Ninth
Amendment to Credit Agreement and Acknowledgment, dated as of April 21, 1997,
the Tenth Amendment to Credit Agreement and Assignment, dated as of June 25,
1997, the Eleventh Amendment to Credit Agreement and Limited Waivers, dated as
of October 20, 1997, the Twelfth Amendment to Credit Agreement, dated as of
January 13, 1998, the Thirteenth Amendment to Credit Agreement, dated as of July
20, 1998, the Fourteenth Amendment to Credit Agreement, dated as of December 11,
1998, the Fifteenth Amendment to Credit Agreement, dated as of February 23,
1999, the Sixteenth Amendment to Credit Agreement, dated as of March 26, 1999;
and the Seventeenth Amendment to Credit Agreement, dated as of September 24,
1999 (the "Credit Agreement"); and

         WHEREAS, the parties hereto have agreed to amend the Credit Agreement
as herein provided;

         NOW, THEREFORE, the parties hereto agree as follows:

         Section 1. Amendments to Credit Agreement.

   1.1   Amendments to Article I: Definitions and Accounting Terms.


         A. Subsection 1.1 of the Credit Agreement is hereby amended by amending
subsection (a) of the definition of "Change of Control" contained therein to
read in its entirety as follows:

         "(a) MAXXAM not owning (other than by reason of the existence of a Lien
or other encumbrance but including by reason of the foreclosure of or other
realization upon a Lien or other encumbrance) direct or indirect sole beneficial
ownership (as defined under Regulation 13d-3 of the Securities Exchange Act of
1934 as in effect on the date of this Agreement) of at least 40% of the total
common equity, on a fully diluted basis, of the Parent Guarantor or the Company;
or"

         B. Subsection 1.1 of the Credit Agreement is hereby amended by amending
the definition of "Minimum Net Worth" contained therein to read in its entirety
as follows:

         "'Minimum Net Worth' means (a) for each Fiscal Quarter of the Company
ending on or prior to December 31, 1998 (commencing with the Fiscal Quarter
ending September 30, 1996), $500,000,000 plus 50% of Net Income (but not loss)
for each such Fiscal Quarter, (b) for the two Fiscal Quarters of the Company
ending on March 31, 1999 and June 30, 1999, $600,000,000 plus 50% of Net Income
(but not loss) for each such Fiscal Quarter, and (c) for each Fiscal Quarter of
the Company ending thereafter, $550,000,000 plus 50% of Net Income (but not
loss) for each such Fiscal Quarter; provided that the calculation of Minimum Net
Worth shall exclude (i) the effect of any non-cash charges, up to an aggregate
amount of $70,000,000, in respect of the Micromill project, including (without
limitation) any write-down of Micromill project assets located at the Center for
Technology in Pleasanton, California, and at the Micromill facility near Reno,
Nevada, (ii) the net cumulative effect of any mark-to-market gains or losses
incurred after December 31, 1998, up to an aggregate net amount of $50,000,000
of losses, on aluminum hedging agreements of the Company and its Subsidiaries
that do not qualify for hedging treatment under GAAP, (iii) the effect of any
non-cash charges, up to an aggregate amount of $30,000,000, in respect of the
settlement of the Company's labor dispute with the United Steelworkers of
America, and (iv) the net cumulative effect of any gains or losses, up to an
aggregate net amount of $50,000,000 of losses, in respect of adjustments to the
net cost basis of the assets of the Gramercy, Louisiana facility as a result of
the explosion at such facility, all of the above adjustments to be reflected on
the relevant Compliance Certificate."
<PAGE>   2

         Section  2. Conditions to Effectiveness.

         This Amendment shall become effective as of the date hereof only when
the following conditions shall have been satisfied and notice thereof shall have
been given by the Agent to the Parent Guarantor, the Company and each Lender
(the date of satisfaction of such conditions and the giving of such notice being
referred to herein as the "Eighteenth Amendment Effective Date"):

         A. The Agent shall have received for each Lender counterparts hereof
duly executed on behalf of the Parent Guarantor, the Company, the Agent and the
Required Lenders (or notice of the approval of this Amendment by the Required
Lenders satisfactory to the Agent shall have been received by the Agent).

         B. The Agent shall have received:

                  (1) Resolutions of the Board of Directors or of the Executive
Committee of the Board of Directors of the Company and the Parent Guarantor
approving and authorizing the execution, delivery and performance of this
Amendment, certified by their respective corporate secretaries or assistant
secretaries as being in full force and effect without modification or amendment
as of the date of execution hereof by the Company or the Parent Guarantor, as
the case may be;

                  (2) A signature and incumbency certificate of the officers of
the Company and the Parent Guarantor executing this Amendment;

                  (3) For each Lender, an opinion, addressed to the Agent and
each Lender, from Kramer Levin Naftalis & Frankel LLP, in form and substance
satisfactory to the Agent; and

                  (4) Such other information, approvals, opinions,
documents or instruments as the Agent may reasonably request.

         Section  3. Company's Representations and Warranties.

         In order to induce the Lenders and the Agent to enter into this
Amendment and to amend the Credit Agreement in the manner provided herein, the
Parent Guarantor and the Company represent and warrant to each Lender and the
Agent that, as of the Eighteenth Amendment Effective Date, after giving effect
to the effectiveness of this Amendment, the following statements are true and
correct in all material respects:

         A. Authorization of Agreements. The execution and delivery of this
Amendment by the Company and the Parent Guarantor and the performance of the
Credit Agreement as amended by this Amendment (the "Amended Agreement") by the
Company and the Parent Guarantor are within such Obligor's corporate powers and
have been duly authorized by all necessary corporate action on the part of the
Company and the Parent Guarantor, as the case may be.

         B. No Conflict. The execution and delivery by the Company and the
Parent Guarantor of this Amendment and the performance by the Company and the
Parent Guarantor of the Amended Agreement do not:

                  (1) contravene such Obligor's Organic Documents;

                  (2) contravene the Senior Indenture, the New Senior Indenture,
the Additional New Senior Indentures, or the Subordinated Indenture or
contravene any other contractual restriction where such a contravention has a
reasonable possibility of having a Materially Adverse Effect or contravene any
law or governmental regulation or court decree or order binding on or affecting
such Obligor or any of its Subsidiaries; or

                  (3) result in, or require the creation or
imposition of, any Lien on any of such Obligor's properties or any of the
properties of any Subsidiary of such Obligor, other than pursuant to the Loan
Documents.

         C. Binding Obligation. This Amendment has been duly executed and
delivered by the Company and the Parent Guarantor and this Amendment and the
Amended Agreement constitute the legal, valid and binding obligations of the
Company and the Parent Guarantor, enforceable against the Company and the Parent
Guarantor in accordance with their respective terms, except as may be limited by
bankruptcy, insolvency, reorganization, moratorium or similar laws relating to
or limiting creditors' rights generally and by general principles of equity.

         D. Governmental Approval, Regulation, etc. No authorization or approval
or other action by, and no notice to or filing with, any governmental authority
or regulatory body or any other Person is required for the due execution,
delivery or performance of this Amendment by the Company or the Parent
Guarantor.

         E. Incorporation of Representations and Warranties from Credit
Agreement. Each of the statements set forth in Section 7.2.1 of the Credit
Agreement is true and correct.

         Section 4. Acknowledgement and Consent.

         The Company is a party to the Company Collateral Documents, in each
case as amended through the date hereof, pursuant to which the Company has
created Liens in favor of the Agent on certain Collateral to secure the

<PAGE>   3

Obligations. The Parent Guarantor is a party to the Parent Collateral Documents,
in each case as amended through the date hereof, pursuant to which the Parent
Guarantor has created Liens in favor of the Agent on certain Collateral and
pledged certain Collateral to the Agent to secure the Obligations of the Parent
Guarantor. Certain Subsidiaries of the Company are parties to the Subsidiary
Guaranty and/or one or more of the Subsidiary Collateral Documents, in each case
as amended through the date hereof, pursuant to which such Subsidiaries have (i)
guarantied the Obligations and/or (ii) created Liens in favor of the Agent on
certain Collateral. The Company, the Parent Guarantor and such Subsidiaries are
collectively referred to herein as the "Credit Support Parties", and the Company
Collateral Documents, the Parent Collateral Documents, the Subsidiary Guaranty
and the Subsidiary Collateral Documents are collectively referred to herein as
the "Credit Support Documents".


         Each Credit Support Party hereby acknowledges that it has reviewed the
terms and provisions of the Credit Agreement as amended by this Amendment and
consents to the amendment of the Credit Agreement effected as of the date hereof
pursuant to this Amendment.

         Each Credit Support Party acknowledges and agrees that any of the
Credit Support Documents to which it is a party or otherwise bound shall
continue in full force and effect. Each Credit Support Party hereby confirms
that each Credit Support Document to which it is a party or otherwise bound and
all Collateral encumbered thereby will continue to guaranty or secure, as the
case may be, the payment and performance of all obligations guaranteed or
secured thereby, as the case may be.

         Each Credit Support Party (other than the Company and the Parent
Guarantor) acknowledges and agrees that (i) notwithstanding the conditions to
effectiveness set forth in this Amendment, such Credit Support Party is not
required by the terms of the Credit Agreement or any other Loan Document to
consent to the amendments to the Credit Agreement effected pursuant to this
Amendment and (ii) nothing in the Credit Agreement, this Amendment or any other
Loan Document shall be deemed to require the consent of such Credit Support
Party to any future amendments to the Credit Agreement.

         Section 5. Miscellaneous.

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

                  (1) On and after the Eighteenth 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 Amended Agreement.

                  (2) 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.

         B. Applicable Law. THIS AMENDMENT SHALL BE DEEMED TO BE A CONTRACT MADE
UNDER AND GOVERNED BY THE INTERNAL LAWS OF THE STATE OF NEW YORK, WITHOUT GIVING
EFFECT TO SUCH LAWS RELATING TO CONFLICTS OF LAWS.

         C. Headings. The various headings of this Amendment are inserted for
convenience only and shall not affect the meaning or interpretation of this
Amendment or any provision hereof.

         D. Counterparts. This Amendment may be executed by the parties hereto
in several counterparts and by the different parties on separate counterparts,
each of which shall be deemed to be an original and all of which shall
constitute together 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.

         E. Severability. Any provision of this Amendment which is prohibited or
unenforceable in any jurisdiction shall, as to such provision and such
jurisdiction, be ineffective to the extent of such prohibition or
unenforceability without invalidating the remaining provisions of this Amendment
or affecting the validity or enforceability of such provisions in any other
jurisdiction.

         IN WITNESS WHEREOF, this Amendment has been duly executed and delivered
as of the day and year first above written.


KAISER ALUMINUM CORPORATION              KAISER ALUMINUM & CHEMICAL CORPORATION


By: /S/ Karen A. Twitchell               By: /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed:  Karen A. Twitchell
Its:  Treasurer                          Its:  Treasurer

BANK OF AMERICA, N.A. (successor to      BANK OF AMERICA, N.A. (successor to
BankAmerica Business Credit, Inc.),      BankAmerica Business Credit, Inc.)
as Agent

By: /S/ Michael J. Jasaitis              By:  /S/ Michael J. Jasaitis
Name: Michael J. Jasaitis                Name: Michael J. Jasaitis
Its: Vice President                      Its: Vice President
<PAGE>   4
BANK OF AMERICA, N.A. (formerly known    THE CIT GROUP/BUSINESS
as Bank of America National Trust and    CREDIT, INC.
Savings Association)

By:  /S/ Michael Balok                   By:  /S/ Grant Weiss
Name Printed: Michael Balok              Name Printed:  Grant Weiss
Its: Managing Director                   Its:  Assistant Vice President


CONGRESS FINANCIAL CORPORATION           HELLER FINANCIAL, INC.
(WESTERN)

By: /S/ Kristine Metchikian              By:  /S/ Richard J. Holston
Name Printed:  Kristine Metchikian       Name Printed:  Richard J. Holston
Its: Vice President                      Its:  Assistant Vice President


LA SALLE BANK NATIONAL                   TRANSAMERICA BUSINESS CREDIT
ASSOCIATION (formerly known as           CORPORATION
La Salle National Bank)

By:  /S/ Douglas C. Colletti             By:  /S/ Robert Heinz
Name Printed: Douglas C. Colletti        Name Printed:  Robert Heinz
Its:  First Vice President               Its:  Senior Vice President

ABN AMRO BANK N.V.


By: /S/ Jeffrey A. French
Name Printed:  Jeffrey A. French
Its:  Senior Vice President


By:  /S/ Robert S. Sheppard
Name Printed:  Robert S. Sheppard
Its:  Vice President

ACKNOWLEDGED AND AGREED TO:

AKRON HOLDING CORPORATION                KAISER ALUMINUM & CHEMICAL
                                         INVESTMENT, INC.

By: /S/ Karen A. Twitchell               By: /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed:  Karen A. Twitchell
Its:  Treasurer                          Its:  Treasurer

KAISER ALUMINUM PROPERTIES,              KAISER ALUMINUM TECHNICAL
INC.                                     SERVICES, INC.

By: /S/ Karen A. Twitchell               By:  /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed:  Karen A. Twitchell
Its:  Treasurer                          Its:  Treasurer

OXNARD FORGE DIE COMPANY, INC.           KAISER ALUMINIUM
                                         INTERNATIONAL, INC.

By: /S/ Karen A. Twitchell               By:  /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed:  Karen A. Twitchell
Its:  Treasurer                          Its:  Treasurer

KAISER ALUMINA AUSTRALIA                 KAISER FINANCE CORPORATION
CORPORATION

By:  /S/ Karen A. Twitchell              By:  /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed:  Karen A. Twitchell
Its:  Treasurer                          Its:  Treasurer

ALPART JAMAICA INC.                      KAISER JAMAICA CORPORATION

By:  /S/ Karen A. Twitchell              By:  /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed:  Karen A. Twitchell
Its:  Treasurer                          Its:  Treasurer

KAISER BAUXITE COMPANY                   KAISER EXPORT COMPANY

By:  /S/ Karen A. Twitchell              By:  /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed:  Karen A. Twitchell
Its:  Treasurer                          Its:  Treasurer

KAISER MICROMILL HOLDINGS, LLC           KAISER SIERRA MICROMILLS, LLC

By:  /S/ Karen A. Twitchell              By:  /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed: Karen A. Twitchell
Its:  Treasurer                          Its: Treasurer

KAISER TEXAS SIERRA MICROMILLS,          KAISER TEXAS MICROMILL
LLC                                      HOLDINGS, LLC

By:  /S/ Karen A. Twitchell              By:  /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed:  Karen A. Twitchell
Its:  Treasurer                          Its:  Treasurer

KAISER BELLWOOD CORPORATION              KAISER TRANSACTION CORP.

By:  /S/ Karen A. Twitchell              By:  /S/ Karen A. Twitchell
Name Printed:  Karen A. Twitchell        Name Printed:  Karen A. Twitchell
Its:  Treasurer                          Its:  Treasurer