A fugitive Georgetown accountant who was indicted in an investment-fraud scheme was arrested Sunday in Ireland, one day after an extradition treaty took effect, the U.S. attorney's office in Washington said yesterday.

Charles J. Walsh, 36, was one of four U.S. fugitives taken into custody by Irish authorities, according to U.S. Attorney Joseph E. diGenova, who went to Ireland about 10 days ago to coordinate preparations for Walsh's arrest.

Walsh, former head of Charles Walsh & Partners, a financial advisory firm at 3062 M St. NW, was indicted last May by a federal grand jury here in connection with a tax-fraud scheme that allegedly cost the U.S. Treasury $6.8 million and netted $2.5 million for Walsh.

The indictment charged that the plan involved the leasing of mostly nonexistent marine shipping containers to some 300 unsuspecting investors, who took income tax credits and deductions on them.

The investors lost their money and have been required to pay back the taxes owed, plus interest and penalties, according to federal prosecutors.

Two business associates of Walsh's, Kenneth I. Brown, 52, and Algis Pabarcius, 52, pleaded guilty earlier this year in connection with the case. Brown was sentenced to four years in prison and Pabarcius to three years. Both received $10,000 fines.

In a second, 29-count indictment, handed down on Dec. 6 and unsealed yesterday, Walsh was charged in another alleged fraud involving 118 investors who were bilked of some $600,000 between May 1980 and December 1982.

Prosecutors charged that the scheme, operating under the names "Trading Strategies and Parallel Positions in U.S. Treasury Instruments" and "The Vanguard Bond Fund," involved arbitrage transactions in U.S. securities.

The operation allegedly used a fake bank set up on the island of Monserrat in the British West Indies, according to the indictment.

Prosecutors said both alleged operations involved a complicated web of "offshore" corporations in countries where secrecy laws helped hide Walsh's alleged ownership and gave investors the impression the companies were legitimate.

Walsh, who is under $5 million bond on each of the two indictments, is scheduled for a bond hearing on Friday in Ireland and an extradition hearing within 18 days.