Sen. Charles McC. Mathias, chairman of a select Senate committee probing the FBI's Abscam investigation techniques, revealed yesterday that middlemen had named 44 public officials--23 members of Congress and 21 state and local officials--other than those already indicted and tried as willing to accept bribes.

The allegations were eventually found to be groundless, the product of bragging by middlemen who did not realize they were working for the FBI. But some officials' names were leaked to the press, damaging reputations.

As the Senate committee began its inquiry yesterday, Assistant FBI Director Oliver B. Revell, head of the Criminal Investigative Division, was asked to explain the FBI's undercover guidelines and why the FBI accepted the word of known criminals and con men in the investigation.

"Our mandate in this inquiry is not to punish the executive branch of government, not to exempt members of Congress from the application of any proper and effective law enforcement technique and not to terminate the use of undercover operations," Mathias (R-Md.) said as the session began in the historic Senate Caucus Room where the Watergate hearings were conducted.

But other members asked whether the FBI had violated the rights of those public officials who were named but were never offered bribes.

Revell, testifying that "undercover operations are lawful, they are indispensable and they are effective," reminded the senators that the FBI used the same guidelines and procedures in Abscam as it does in all undercover investigations, including those involving narcotics, organized crime, and terrorism.

He explained that the middlemen who caused much of the trouble were brought into the scheme by informants and had no idea they were working for the FBI. Although the FBI was able to manipulate them through threats and promises, it was impossible to keep complete tabs on them, he said.

He said controls over Abscam were the strictest of any law enforcement operation in the United States. Only FBI Director William H. Webster can approve a bribe offer to an elected federal official, he said.

In response to questioning, Revell said it was impossible for the FBI to dismiss the lying middlemen without compromising the investigation.

"You have to maintain the cover of the operation. You can't say, 'I'm an FBI agent and you misled me,' " Revell said.

He said that in the murky world of underworld informants and double dealing, the FBI does not always get the truth.

"That's not the real world," Revell said. "We can't depend on the representations of criminals--many of which are true--to all be true."

The select committee was formed last spring after Harrison A. Williams Jr. (D-N.J.) resigned from the Senate. He was the only senator and the last of seven members of Congress charged in the operation, in which FBI agents posed as representatives of Arab sheiks and offering bribes for promises of legislative favors.

The committee plans to investigate the FBI's undercover techniques in Abscam and whether the results justified the cost. James F. Neal, a former Watergate prosecutor, has been hired to run the investigation.