Alvin C. Frost, the embattled D.C. senior government financial analyst who had publicly accused his superiors of wrongdoing and was placed on administrative leave for changing the password to a city computer system, said last night he has been fired by the city.

Frost said he had received a hand-delivered letter from City Administrator Thomas Downs that gave the reason for the dismissal as his "willful mutilation and alteration of official government records." The letter also cited "dishonesty" and "insubordination, to wit, refusal to comply with written instructions and direct orders by your superiors," Frost said.

Downs could not be reached for comment last night, and D.C. Deputy Mayor Alphonse G. Hill, who had earlier described Frost as "a nerd and an imbecile," refused to comment.

Downs placed Frost on administrative leave on Feb. 14, two weeks after he altered a secret access code to computerized city financial records, an action Frost said he took to prevent superiors from destroying records or tampering with his personal files.

Frost refused to reveal the new code, and city officials called in computer experts to regain access to the computer. Frost's superiors then changed the locks on his office and briefly transferred him to another job before he was placed on leave.

Frost said last night he believes that his dismissal was a move to silence his criticisms of the Barry administration and shift attention from his allegations of corruption and incompetence in the management of city financial affairs.

"They only had one thing they could seize on and that was the password, and that became a major issue." Frost said. "They were just waiting for any excuse to fire me."

Frost, 38, a government employe since 1982, said he is planning to contest the firing and that he was told in the letter he had 15 days in which to make a written appeal.

"I believe the dismissal is illegal because the reasons they give and the statements they made in the letter are inaccurate and untrue. They are lies . . . ," Frost said

If he wins that appeal and is reinstated, Frost said he will still resign and sue the city for damages.

Frost first came to public attention last year when he alleged that Assistant D.C. Treasurer Fred Williams ignored warnings and invested $100 million in a New Jersey-based securities firm. The firm, Bevill Bresler & and Schulman Inc., subsequently went bankrupt, but the city funds were recovered.

It was learned later that Williams, who had been Frost's supervisor, had backdated a memorandum concerning the financial stability of the company.

City Council member John A. Wilson (D-Ward-2) last week called for Williams to be dismissed for backdating the memo, and Wilson criticized him along with deputy mayor Hill and D.C. Controller N. Anthony Calhoun for being "derelict" in their handling of city funds.

Last month Williams asked to be reassigned because of the publicity generated by his clashes with Frost, and he is now working in an unspecified position in the city's finance and revenue office.