The Nicaraguan government has asked federal prosecutors in Washington to bring criminal charges against Francisco Fiallos, the former Nicaraguan ambassador, for allegedly absconding with $619,000 from an embassy bank account after he resigned and denounced the ruling Sandinista regime as a "tyranny."

Nicaraguan Minister of Justice Carlos Arguello said at a press conference yesterday that he met Tuesday with Principal Assistant U.S. Attorney Joseph diGenova after attorneys for Fiallos acknowledged that despite his earlier denials, the former ambassador did have the money.

The diplomatic flap over the missing embassy funds has escalated in the past week into a series of international propaganda exchanges, embarrassed the Nicaraguan opposition movement and entangled three prominent Washington law firms in negotiations for the return of the money. Meanwhile, Fiallos is in hiding and not available for comment.

Arguello said that at his meeting with federal prosecutors he "presented conclusive evidence of . . . criminal offenses" by Fiallos, a Harvard-trained lawyer who assumed the ambassadorial post early last year and resigned last month.

DiGenova confirmed that he and Richard Beizer, chief of the office's fraud section, met with Arguello Tuesday. "They made a formal complaint," DiGenova said. "We received the information and we're looking into it."

Nicaraguan officials have withdrawn Fiallos' diplomatic immunity.

The money in question represents most of the proceeds from the April 1982 sale of the once-elegant Nicaraguan ambassadoral residence on Ellicott Street NW that was boarded up and later fire-damaged after the Sandinistas took power by ousting the government of Gen. Anastasio Somoza, including his ambassador to Washington, Guillermo Sevilla-Secasa.

In an interview with The Washington Post earlier this month, Fiallos called the charges a "slanderous lie" and denied taking the money. He maintained in the interview that he had withdrawn the money from the Riggs National Bank under coded instructions sent to him by the Nicaraguan foreign ministry and turned it over to an emissary for delivery to the Central American nation.

The Nicaraguan justice minister said yesterday, however, that attorneys for Fiallos contacted the embassy's Washington law firm, last Friday and again on Monday, "and admitted that Mr. Fiallos never gave any money to a government emissary and that he still has the $618,516.37."

Arguello said that in these two telephone conversations, Fiallos' attorneys said the ex-ambassador was willing to return the money if the Nicaraguan government was willing to "formally absolve him of all liability and responsibility for his actions."

An attorney involved in the Nicaraguan legal action said that Fiallos' offer was forcefully rejected and that demands were made for the immediate return of the money.

Nicaraguan officials later identifed Fiallos' attorneys as Samuel R. Berger and Sherwin J. Markman of the Hogan & Hartson law firm. A spokesman said the attorneys made the statements on behalf of the former ambassador to Paul S. Reichler and Stuart E. Eizenstat, whose firm, Powell, Goldstein, Frazer & Murphy, represents the Nicaraguan embassy.

Reichler said that earlier this week, the Nicaraguans were notified that Hogan & Hartson had withdrawn from representing Fiallos and that his new attorney was Brendan V. Sullivan Jr. of the Williams & Connolly law firm.

Markman could not be reached for comment, but Berger said, "In view of the fact that we no longer represent the ambassador, we feel we should not comment." Sullivan could not be reached for comment.