Justice Department officials began an investigation yesterday to determine how news of an FBI undercover "sting" operation allegedly implicating eight members of Congress in bribery schemes leaked to the press.

Robert M. Smith, a department spokesman, said "the disclosures made by the media are regrettable because they may injure the reputation of innocent people." He added that in light of the nature and extent of the purported disclosures, the department's office of professional responsibility would start an "intensive investigation to see whether deliberate disclosures have been made by federal employes."

Over the weekend, NBC-TV, Newsday, The New York Times and The Washington Post disclosed the investigation in detailed accounts.

The news organizations quoted sources as saying that FBI undercover agents posing as Arab sheiks or their representatives paid hundreds of thousands of dollars in cash to members to Congress or their associates over the past year and a half, and the FBI had videotapes of the transactions.

More than 100 FBI agents conducted hurried interviews Saturday in several states because officials were told that stories were planned.

As it stands, the press has carried detailed descriptions of the allegations before the government has had time even to convene grand juries to hear the evidence. In fact, sources have cautioned that indictments may not result in all eight cases.

But officials familiar with the investigation emphasized yesterday that the decision to shut down the "sting" last weekend had been made before the reporters made official inquiries for their stories.

The decision to close the investigation was made because it was getting too expensive and complex, officials said. Undercover agents had made so many financial commitments to the congressmen and other public officials that they couldn't deliver.

Officials were emphatic in denying that FBI Director William H. Webster was worried about snagging too many members of Congress with the "sting" or was wrapping up the inquiry so indictments and trials could come before the fall elections.

One official suggested that the story may have begun to leak out when the FBI and Justice Department prosecutors had to gather a large force of agents to begin final interviews.

"At some point you just have to draw the line and say we've got enough to take to a grand jury," another said.

Another factor in the decision to shut down was the fear of leaks that actually took place later, one source said.

Attorney General Benjamin R. Civiletti was described as incensed about the detail in the media accounts. Other officials said they were particularly disturbed because a part of an internal document describing the case appeared to have been given to The New York Times.

Leak investigations are a routine department reaction to premature publicity in important cases. But officials involved said yesterday that this internal probe seemed more serious than most.

In past leak investigations, attorneys and agents who had access to the information have been asked to sign affidavits about whether they leaked to reporters. Reporters have not been questioned or subpoenaed.