By Shelley Murphy and Matt Viser, Globe Staff

The wife of US Representative John F. Tierney is poised to plead guilty tomorrow to federal tax charges for managing a bank account that her brother allegedly used to deposit millions of dollars in illegal gambling profits he raked in from an offshore sports betting operation in Antigua.

Patrice Tierney, 59, who is married to the Salem Democrat, is charged with four counts of aiding and abetting the filing of false tax returns by her brother, Robert Eremian, of St. John's, Antigua.

The US Attorney's office said she is scheduled to plead guilty tomorrow afternoon.

In a lengthy statement tonight, Congressman Tierney defended his wife and said she was betrayed by her brother. He said she believed her brother's earnings were from legitimate business, but is pleading guilty because she acknowledges she should have done more to investigate his activities.

''She now realizes that the trust she formerly had in her brother was misplaced,'' John Tierney said. ''I stand by Patrice in this difficult time.''

The news comes as Tierney is in the midst of a reelection campaign, just four weeks before voters go to the polls. The seven-term congressman has been favored against Republican challenger Bill Hudak, a first-time candidate and Boxford lawyer.

Boston attorney Donald K. Stern, who represents Patrice Tierney, said that under a plea agreement, prosecutors will recommend that she receive probation, with several months of home confinement.

But, Stern said, ''I intend to urge the court to impose a sentence of straight probation.''

Prosecutors allege that Eremian 57, moved an illegal gambling business from Lynnfield to Antigua in 1996 and deposited profits from his business, Sports Offshore, an Internet gambling site, into an account at Bank of America in Massachusetts.