William S. Sessions, the Texas federal judge nominated to direct the Federal Bureau of Investigation, promised the Senate Judiciary Committee yesterday he would resist any administration efforts to meddle improperly in investigations and would turn to congressional oversight committees for help if necessary.

Sessions, in a day-long confirmation hearing, also expressed his independence from the Reagan administration on another key matter: the "exclusionary rule," which provides that information obtained improperly by police cannot be used as evidence.

The administration has asked for an exception to the rule when the improper evidence was obtained by police acting "in good faith." But Sessions said, "By and large, I'm happy the way it is, as tough as it is for law enforcement officials, because it protects the rights and privileges of our citizens."

He also said that he supports the Miranda rule under which suspects must be warned of their rights before questioning. Attorney General Edwin Meese III has been quoted as saying that the U.S. Supreme Court's 1966 decision in Miranda v. Arizona should be overturned because it protects the guilty. But Sessions said, "I am convinced the burden is an appropriate one."

Sessions, who has a reputation as a tough, law-and-order judge, is expected to win confirmation overwhelmingly to succeed William H. Webster in the 10-year appointment. Sen. Patrick J. Leahy (D-Vt.) said during the hearing, "This sounds more like a canonization than a confirmation hearing." Not a single witness opposed the nomination.

The Sessions hearing is in sharp contrast to the already bitter battle over Judge Robert H. Bork's nomination to the Supreme Court and was referred to by Sen. Edward M. Kennedy (D-Mass.) as "the lull before the storm. Perhaps, when the Bork controversy is resolved, the administration may wish that it had left Judge Bork on the Court of Appeals and nominated Judge Sessions for the Supreme Court."

Judiciary Committee Chairman Joseph R. Biden Jr. (D-Del.) has promised a vote on Sessions on Tuesday, the day the committee starts its Bork hearings.

Asked how he would handle an improper request from the White House, Sessions said he would take his objections to the attorney general and, if necessary, to the president. If that failed, he said he would confer with congressional oversight committees.

He also said Meese has promised him there will be no such pressure. "I have the assurance of the attorney general of the United States that I may fulfill my oath of office," he said.

Sessions said he would not resign if ordered to do something he considers wrong. "I do not intend to resign, to seek the shelter of resignation."

Sessions did not criticize Meese's failure to bring the FBI into the Iran-contra investigation until after crucial White House documents had been shredded, but he said, "I think it would be appropriate to seek the advice of the FBI . . . once you step outside your agency."

He also promised members of the committee that he would log any contacts between high FBI officials and the White House or Congress.

Sessions' July 24 nomination followed a five-month search for a successor to Webster, a former federal judge who resigned in May to head the Central Intelligence Agency.

Sessions gained national attention in 1982 when he presided over the murder trial of suspects in the slaying of U.S. District Court Judge John H. Wood. Sessions, who refused to remove himself from the case, gave the convicted killer consecutive life terms and sentenced three others to 15- to 30-year terms.