Federal prosecutors expect to bring the first indictments in the Pentagon fraud and bribery scandal just one week after the presidential election and may continue charging people for up to a year. They won't rule out congressmen as targets of the investigation.

Henry E. Hudson, the U.S. attorney in suburban Virginia who is running the multistate, multiagency investigation, is well aware of whispers that the Reagan administration wanted charges delayed until after Nov. 8 so that Democratic presidential nominee Michael Dukakis wouldn't have them as ammunition against George Bush."Nothing would have given me greater pleasure than to hand down indictments in the first part of October," Hudson said at week's end. Indeed, he and his bosses at the Justice Department had predicted that kind of timetable last June when the scandal broke with FBI raids on 44 sites coast-to-coast.

But Hudson said complexity, not politics, pushed the time back. This is the largest case his office has ever handled. His attorneys and investigators have reviewed 700,000 documents and more are still under subpoena to be turned over. They've listened to "thousands and thousands of tapes of two years' of telephone interceptions."

Prosecutors say the 2-year-old investigation into the $150 billion-a-year Pentagon procurement system has turned up evidence that consultants, including some former high-level Reagan administration officials and former high-ranking military men, working for the nation's largest defense contractors bribed Pentagon officials for information vital to winning contracts worth billions of dollars. Five Pentagon employees have been transferred away from contract work.

Hudson's investigators have found foreign or offshore bank accounts tied to some of the principals in the case, and he said they are seeking foreign bank records - "always (a) delicate issue and . . . a time-consuming process."

Also government and defense sources, who won't allow use of their names, indicate Hudson's men have been kept waiting for responses from some potential defendants to offers of plea bargains.

Hudson is using 15 attorneys, including some from the Justice Department's fraud and public integrity sections, and 75 federal agents, from the FBI, the Naval Investigative Service and the Internal Revenue Service. They've been working 10 and 12 hours a day, including weekends.

Now, Hudson said, "I'm very optimistic on mid-November indictments." Justice sources fix the date at Nov. 15, which happens to be next day the grand jury meets.