Two congressional subcommittees are broadening their investigation into allegations that Citibank, the world's second largest bank, violated currency trading and tax laws in Europe.

In a joint letter yesterday to seven federal agencies and law enforcement authorities, the chairmen of a House Banking subcommittee and a House Judiciary subcommittee asked for progress reports on several ongoing investigations of Citibank.

Rep. Joseph Minish (D.-N.J.) and John Conyers Jr. (D-Mich.), respective chairmen of the Banking subcommittee on general oversight, and Judiciary subcommittee on crime, said in their letters that subcommittee officials would be checking the agencies to determine the progress of the investigations. They said they were taking the action "because the seriousness of the charges necessitates a full investigation."

The letters were sent to Treasury Secretary W. Michael Blumenthal, Attorney General Griffin Bell, Federal Reserve Chairman G. William Miller, Comptroller John Heiman, Securities and Exchange Commission Chairman Harold Williams, Internal Revenue Service Commissioner Jerome Kurtz and the U.S. attorney for the Southern District of New York, Robert Fiske Jr.

"We think this case is very heavy," Conyers said in an interview yesterday. "We are going to widen our investigation, possibly leading to joint subcommittee hearings."

"The intent of the letter is not to prejudge anybody's investigation," Conyers said, "just to insure a full and fair hearing, which is in the interest of both the public and Citibank." The letters are also signed by the ranking Republicans on the subcommittees, Charles E. Grassley (R-Iowa) and John Ashbrook (R-Ohio).

The Citibank case grew out of allegations from a former bank officer in Paris who claimed he was fired from the bank for continually attempting to inform his superiors that the bank may have been violating laws in several foreign countries with respect to its currency trading operations.

That employe, David Edwards, filed suit against the bank last year charging Wrongful dismissal and asking some $14 million in damages.

Edwards contended that the bank used a complicated series of "paper" transactions to launder profits from money trading in the bank's European branches in an attempt to reduce the bank's tax liability on profits in those countries.

The bank's European branches would "park" large holdings of foreign currencies at Citibank Nassau (in the Bahamas) in order to avoid various currency control laws concerning the amount of currency each branch would be allowed to hold, Edwards claimed.

He further contended that the bank would also have its European Branches "sell" various currencies to its Nassau office at a paper loss in order to reduce profits subject to taxes in those countries.Nassau has no such taxes, and the branch there would show large profits that Edwards contended were really earned in Europe.

The bank has denied any worngdoing, and several industry sources have said that much of what Citibank is accused of doing is commonplace in the industry, and in a questionable area at worst.

A study commissioned by the bank's board of directors and conducted by the bank's law firm, Shearman and Sterling and accounting firm, Peat, Marwick & Mitchell, revealed, however, that Citibank may have violated tax and currency laws in as many as five of the seven European countries surveyed.