U.S. District Court Judge William S. Sessions, nominated by President Reagan in July to become the director of the Federal Bureau of Investigation, is expected to breeze through his confirmation hearings this week, according to staff sources on the Senate Judiciary Committee.

Two days of hearings have been scheduled for Wednesday and Thursday, with a committee vote on Sessions planned for the morning of Sept. 15, before the committee begins its more contentious hearings on the nomination of Judge Robert H. Bork to the Supreme Court.

Committee sources said no witnesses have signed up to testify against Sessions. Instead, many police organizations, including the International Association of Chiefs of Police and the Federal Law Enforcement Officers Association, have asked to testify in his favor.

Sessions, who will be first to testify, will face intense questioning, the sources said, on how he plans to run the bureau, his views on safeguarding individual rights, constitutional concerns and his plans for undercover operations.

Congress has been especially concerned about FBI undercover operations since 1979 when several of its members were ensnared in the FBI Abscam investigations. Several members of Congress were indicted and convicted.

Committee sources said their long background investigation of Sessions, chief judge of the U.S. District Court for the western district of Texas, has turned up no substantive negative information.

Sessions, 57, who has a tough, law-and-order reputation, is best known for his work on the bench in the late 1970s and early 1980s following the murder of U.S. District Court Judge John H. Wood Jr., known as "maximum John" for the tough sentences he imposed on drug dealers. Wood was the first federal judge to be murdered in more than a century.

Sessions took over the drug-trafficking trial Wood had been scheduled to handle, and two years later, he presided over the trial of Wood's murderers. He imposed two life terms on the convicted killer, and sentences of five to 30 years for the other three defendants.

A native of Fort Smith, Ark., Sessions worked in private practice in Waco, Texas, for 10 years before being named U.S. attorney in 1971 by President Richard M. Nixon. He was named to the federal bench by President Gerald R. Ford in 1974.

His nomination to the FBI was announced by the White House July 24 after a politically embarrassing search of almost five months during which several candidates reportedly turned down the position.

If he is approved, as expected, Sessions will replace former director William H. Webster, who became director of the Central Intelligence Agency in May.

Since then, the bureau has been run on an acting basis by John Otto, a 23-year FBI veteran who is an executive assistant director of the bureau.

FBI insiders have been very supportive of the Sessions nomination, describing him as a well-known "friend of law enforcement."

Otto said recently that Webster sat down with his top management team, before he left the FBI, and drew up a three-year operating plan with priorities including counterterrorism, organized crime, public corruption investigations, labor racketeering and computer crime.

Otto said that while waiting for the new director, FBI officials have been trying to keep the bureau on the course set by Webster during his nine years as director.