John M. Rusnak, the former currency trader for Allfirst Financial Inc. whose transactions led to $691.2 million in losses and presaged a purge of the bank's top management, is expected to plead guilty today to a criminal charge of bank fraud, informed sources have confirmed.

Rusnak, who pleaded not guilty to seven counts of bank fraud in June, is scheduled to appear in federal court this morning. U.S. Attorney Thomas M. DiBiagio released a statement saying that "a guilty plea in a significant financial fraud case" will be announced at a news conference later in the day.

Sources said yesterday that, barring a last-minute snag, the plea will come from Rusnak.

No formal agreement has been filed with the court, and no other details could be learned.

Rusnak has cooperated with investigators since the currency trading scandal at Allfirst unraveled in February. Aside from salary bonuses, Rusnak is not thought to have benefited financially from the suspected fraud. Those factors should weigh in his favor in negotiations with prosecutors, legal experts said yesterday.

The Mount Washington resident is accused of ringing up $691.2 million in losses - one of the largest such figures in banking history - mostly by creating a fraudulent paper trail to hide losses from previous trades.

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Lawyers and officials familiar with the federal laws concerning white-collar crime say any plea agreement with Rusnak is likely to include prison time.

"Assuming the loss is anywhere near what has been reported, I think it is a virtual certainty that he faces substantial incarceration," said Herbert Better, a criminal defense lawyer who is a partner at Zuckerman Spaeder LLP in Baltimore. "You could very comfortably say several years."

Robert A. Mintz, head of the white-collar crime and government investigations practice at McCarter & English LLP in Newark, N.J., said, "Typically, the only way that somebody could have any hope of avoiding jail in a case like this would be if they were cooperating with some ongoing criminal investigation. And that doesn't seem to be the case here."

DiBiagio would only confirm that he will hold an 11 a.m. news conference.

Rusnak's attorney, David Irwin, also declined to comment. "If there is a resolution of the case, then I will be glad to comment after that," Irwin said.

Mintz, Better and other experts said a guilty plea is a common outcome in a case such as Rusnak's because federal sentencing guidelines allow defendants to cut as much as five years off their sentences by pleading guilty instead of going to trial.

Rusnak, who will turn 38 Oct. 30, is scheduled for a jury trial in February and could face as much as 30 years in prison. Sources close to the case have long said a plea was likely.

The length of any prison term would be determined by a federal judge using rigid and complicated sentencing guidelines, legal experts said.

Though Rusnak could expect some reduction in his sentence because he is cooperating and doesn't have a criminal record, the guidelines are based mostly on the amount of money lost in the crime. And the amount involved in his suspected fraud is more than six times the largest sum the guidelines contemplate.

"He is going to get substantial jail time for a loss like that" under the guidelines, said Christopher B. Mead, a Washington defense attorney who specializes in white-collar crime. "Even with cooperation, even with a plea of guilty, the amount of the loss results in a very severe guideline sentence. What matters is what he did, and this is a serious crime."

The trading losses attributed to Rusnak have had broad reverberations outside the courtroom, particularly in the boardroom of Allfirst.

Executives at the Baltimore-based bank fired Rusnak when they discovered his suspected trading fraud in February, later accusing him of a "complex and sophisticated" scheme to subvert the bank's internal controls. Six employees related to Rusnak's trading, some of them executives, also were fired.

The bank's Dublin-based parent company, Allied Irish Banks PLC, sent Eugene C. Sheehy to Baltimore to take over for former Chairman Frank P. Bramble, who took early retirement after the scandal broke. Susan C. Keating, Allfirst's president and chief executive, stepped down in July.

Late last month, Allied Irish officials announced that they would sell Allfirst to M&T Bank Corp. of Buffalo, N.Y., in a $3.1 billion deal that they say is unrelated to the Rusnak scandal.