Assistant D.C. Treasurer Fred Williams, supervisor of a senior analyst who changed the password to the city's cash management computer system two weeks ago, has been given new duties following his request for reassignment, D.C. finance officials said yesterday.

Williams has been detailed to an unspecified position in the Department of Finance and Revenue, according to the officials.

The disclosure of Williams' reassignment came a day after City Council Chairman David A. Clarke said Williams should be disciplined for backdating a memorandum submitted at a council hearing last spring.

Council member John A. Wilson (D-Ward 2) said Williams "should be fired."

Alphonse G. Hill, deputy mayor for finance, declined to comment yesterday on Williams, but noted that Williams' request for reassignment was submitted last Friday, four days before Clarke and Wilson made their comments.

Williams was a principal in the clash with Alvin C. Frost, the senior cash management analyst who changed the password to the computer system after raising questions about the city's awarding of financial services contracts and urging Mayor Marion Barry to suspend Hill, Williams and two other city financial officers.

Frost said Friday that he intended to resign next month and that he might run for political office. The same day, city officials announced that he had been placed on administrative leave for insubordination.

Williams, who was reassigned effective Tuesday, said he wanted a new job because the "controversy involving myself and Alvin C. Frost has taken a tremendous toll on the morale and well-being" of his associates. "It appears that the media have been suckered by Mr. Frost into a nonending dialogue which will undoubtedly end only when Mr. Frost receives some kind of personal satisfaction . . . ," he wrote.

Williams denied any wrongdoing and listed a series of accomplishments during his tenure as the $39,000-a-year head of the cash management and treasury operations.

Frost yesterday called Williams' letter "absurd." Williams could not be reached for comment.

William Kao, another assistant D.C. treasurer, will assume Williams' duties, officials said.

The clash between Williams and Frost surfaced last spring during hearings held to examine the city's investment of nearly $100 million with the New Jersey-based securities firm of Bevill, Bresler and Schulman Inc. The firm went bankrupt but the city was able to recoup its investment.

It was disclosed during the hearings that a memo prepared by Williams that justified investing with the firm had been written in April 1985 but backdated to Dec. 7, 1984. Hill said at the time that the document reflected conversations that occurred in December 1984.

Frost testified during the hearings that Williams had pressured him to do business with that securities firm despite his reservations.

Hill, in an interview yesterday, said neither Clarke nor Wilson had followed up the hearings last spring with a letter containing their concerns about Williams. "If they felt so strongly, why wasn't there any letter?" Hill asked.