A U.S. grand jury in the District of Columbia is investigating a Brazilian couple suspected of embezzling $1.55 million from a Washington money market fund in May, a federal prosecutor said yesterday.

Assistant U.S. Attorney Thomas J. Tourish Jr. said the panel's probe of Vera Lucia Campos and Andre L. Prestes, is expected to be completed in about two weeks.

Officials of First Variable Rate Fund for Government Income Inc. have alleged in a civil law suit that Campos, a fund employe, illegally transferred the money by computer on May 5 to Prestes' account at the Rosslyn branch of Virginia National Bank.

Campos and Prestes returned to Brazil shortly after the alleged theft and have blamed the incident on a computer error. Tourish declined to say yesterday whether efforts have been initiated to seek the couple's return to Washington.

In a related development, a Virginia National Bank official said yesterday that money in checking accounts at the Rosslyn branch belonging to Campos and Prestes has been frozen and that a safety deposit box rented by Prestes has been sealed.

According to bank statements filed in U.S. Magistrate's Court in Alexandria, Prestes' account holds $258.88 and Campos' holds $782.11.

A court hearing on the fund's request for return of the $1.55 million, which Prestes allegedly had transferred to a Swiss bank account, has been set for Sept. 4 in Alexandria. That account has been frozen by Swiss officials.