The House ethics committee, responding quickly to new allegations of sexual misconduct by Rep. Donald E. "Buz" Lukens (R-Ohio), yesterday revived an earlier ethics investigation of Lukens stemming from his conviction on a misdemeanor sex charge and ordered him to appear before the panel today.

Lukens, 59, had been the subject of an ethics probe following his 1989 criminal conviction by an Ohio court for having sex with an underage girl, but the panel had not been expected to complete the case because the Ohio lawmaker was defeated in his primary reelection bid last May.

However, the committee abruptly reopened the inquiry yesterday after a Capitol elevator operator alleged to her superiors that Lukens had made what the panel termed "unwanted and unsolicited sexual advances" toward her. The Associated Press reported that Lukens allegedly fondled and propositioned a young elevator operator and gave her his business card in an incident last week.

In renewing its earlier case just a few days before Lukens would have ended his congressional career, the 12-member ethics panel took the unusual step of stripping him of some of his defense rights under House rules and ordered him to appear this afternoon.

Lukens, who has served in the House from 1967 to 1971 and since 1986, could not be reached for comment. His office issued a statement that Lukens, on attorneys' advice, would not comment until more was known about the new allegation.

Lukens's conviction on the Ohio sex charge, for which he was sentenced to 30 days in jail and fined $500, was upheld by an appeals court in June. Lukens is appealing to the Ohio Supreme Court.

Yesterday's reopening of the case by the ethics committee is unusual, and it reflects general concern in Congress over the public's sinking regard for the institution. It is almost unheard of for the panel to summarily waive some of the defense rights normally accorded a member under House rules.

Rumors of the latest incident involving Lukens swept through the Capitol yesterday, and the panel met in an unscheduled session to reopen the probe.

That indicates that the committee is determined to push the case to a conclusion before Congress adjourns, probably this week. That could lead to a floor vote this week if the panel recommends he be reprimanded, censured or expelled.

It is also possible that the committee may simply urge Lukens to resign, said one House source.