Exhibit 31.3Page 1 of 2

RULE
13a-14(a)/15d-14(a) CERTIFICATIONOF PRINCIPAL EXECUTIVE OFFICER OF UNION ELECTRIC
COMPANY(required by Section 302 of the Sarbanes-Oxley Act of 2002)

I,
Gary L. Rainwater, certify that:

1.       
          I have reviewed this report on Form 10-K for the fiscal year ended
          December 31, 2003 of Union Electric Company;

2.       
          Based on my knowledge, this report does not contain any untrue statement of a
          material fact or omit to state a material fact necessary to make the statements
          made, in light of the circumstances under which such statements were made, not
          misleading with respect to the period covered by this report;

3.       
          Based on my knowledge, the financial statements, and other financial information
          included in this report, fairly present in all material respects the financial
          condition, results of operations and cash flows of the registrant as of, and
          for, the periods presented in this report;

4.       
          The registrants other certifying officer and I are responsible for
          establishing and maintaining disclosure controls and procedures (as defined in
          Exchange Act Rules 13a-15(e) and 15d-15(e)) for the registrant and have:

|a) |  | Designed
such disclosure controls and procedures, or caused such disclosure
                    controls and procedures to be designed under our supervision, to
ensure that                     material information relating to the registrant,
including its consolidated                     subsidiaries, is made known to us by
others within those entities, particularly                     during the period in which
this report is being prepared;
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|b) |  | Evaluated
the effectiveness of the registrants disclosure controls and
                    procedures and presented in this report our conclusions about the
effectiveness                     of the disclosure controls and procedures, as of the
end of the period covered                     by this report based on such evaluation;
and
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|c) |  | Disclosed
in this report any change in the registrants internal control
                    over financial reporting that occurred during the registrants
most recent                     fiscal quarter (the registrants fourth fiscal
quarter in the case of an                     annual report) that has materially
affected, or is reasonably likely to                     materially affect, the registrants
internal control over financial                     reporting; and
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5.       
          The registrants other certifying officer and I have disclosed, based on
          our most recent evaluation of internal control over financial reporting, to the
          registrants auditors and the audit committee of registrants board of
          directors (or persons performing the equivalent functions):

|a) |  | All
significant deficiencies and material weaknesses in the design or operation
                    of internal control which are reasonably likely to adversely affect
the                     registrants ability to record, process, summarize and
report financial                     information; and
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Exhibit 31.3Page 2
of 2

|b) |  | Any
fraud, whether or not material, that involves management or other employees
                    who have a significant role in the registrants internal control
over                     financial reporting.
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Date: March 9, 2004

| |  | /s/ Gary L. Rainwater
Gary L. RainwaterChairman, President and Chief Executive Officer(Principal Executive Officer)
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