Displaying occasional humor and unshakable calm, International Olympic Committee President Juan Antonio Samaranch testified for three grueling hours before a congressional subcommittee yesterday in an unprecedented appearance that packed a hearing room on Capitol Hill.

Facing an exhaustive round of questioning from members of the House subcommittee on oversight and investigation, Samaranch seemed eager to relay details of the reform effort that resulted from last year's scandal over the Olympic site selection process. Clearly relaxed, Samaranch sometimes spoke at such length lawmakers felt compelled to interrupt him.

Subcommittee Chair Fred Upton (R-Mich.) and a panel of seven other lawmakers challenged Samaranch on a wide range of matters related to allegations of IOC misconduct, including a $13,000 trip Samaranch's wife made as a guest of the Atlanta committee that bid successfully for the 1996 Olympics.

They also grilled him on the working of the IOC's newly formed ethics commission, a body created to police the organization.

While being criticized for his failure to root out corruption long ago and questioned about the organization's determination to implement the reforms passed this past weekend in Lausanne, Samaranch asserted that the IOC had "cleaned the house" and adopted fundamental changes.

"I can assure you we will deliver what we promised," said Samaranch, IOC president since 1980.

Samaranch agreed to push for action in two areas as a result of persistent questions from lawmakers. He concurred with Rep. Diana DeGette (D-Colo.) that gifts to IOC members should be banned. (New ethics rules state that gifts of nominal value or in accordance with local custom are acceptable.) He also agreed with Rep. Richard Burr (R-N.C.) that the wording of another rule was unclear and should be tightened.

Samaranch maintained, however, that the organization's gift ban should not apply to him, saying that he receives certain gifts on behalf of the organization that are immediately donated to the Olympic Museum in Lausanne.

He also said his wife's all-expenses paid trip to Atlanta with a friend in 1990--the year Atlanta was awarded the '96 Games--was taken at the insistence of bid city officials and received the backing of then-vice president Dan Quayle. Saying his wife was advanced in years and required a travel companion, Samaranch quipped that "I'm not going to tell you how old she is as she would be angry with me."

The most theatrical round of questions came from Rep. Joe Barton (R-Tex.), who suggested in his opening statement that Samaranch use yesterday's congressional forum to resign from his post--a step Samaranch declined to take. Barton referred disparagingly to Samaranch's alleged preference for the title "Your Excellency" and belittled the "crackerjack Olympic investigators" within the IOC.

Barton also attacked Samaranch's statement that the IOC never acted on rumors of corruption in circulation for more than a decade because accusers never "named names."

Samaranch, a 79-year-old Spaniard whose term as IOC president expires in 2001, delivered his opening statement in English but relied on two interpreters during the round of questioning--one who translated subcommittee members' questions into Spanish and another who translated Samaranch's replies into English.

Samaranch asserted that a recent magazine story alleging that his hotel suite in Lausanne cost the IOC $500,000 a year was "a lie." Samaranch, who like all IOC members is an unpaid volunteer, told the Congress that he stays in a normal suite during trips to Lausanne for IOC business at a reduced rate of $250 a day, and that the suite is reserved for him when he is not using it at a rate of $70 a day. The IOC, he said, also pays his travel expenses.

Barton responded by requesting an accounting of Samaranch's personal IOC expenditures.

"I don't think it will be necessary to request that," Samaranch said, adding good-naturedly, "because you can read it in the Los Angeles Times today."

The Los Angeles Times reported on Samaranch's hotel and travel expenses in a story that appeared yesterday.

Later in the day, former senator Howard Baker, a member of the IOC's new ethics commission, told Congress that the commission was a work in progress and was in the midst of choosing an administrative leader and writing its rules and regulations.

Former White House chief of staff Ken Duberstein stood in for former senate majority leader George Mitchell, whose flight failed to arrive in time. Duberstein, who along with Mitchell and other members of a U.S. Olympic Committee-appointed ethics committee suggested in March more than a dozen IOC reforms, said the IOC had instituted dramatic changes but required "close monitoring and frequent checkups."

Former secretary of state Henry Kissinger, a member of the IOC's reform commission, said "there was no proposal we made that was eventually not accepted."

Samaranch was accompanied to the hearing by IOC Director General Francois Carrard; Vice Presidents Anita DeFrantz of the United States and Dick Pound of Canada; and IOC member James Easton from the United States.

Asked after the hearing if he resented Congress's involvement in IOC matters, Samaranch said: "The only thing they did was ask questions to get information. . . . If they ask me to come again, I will come again."