With speculation about the letter’s contents circulating this week, Senator Charles E. Grassley of Iowa, the Republican chairman of the Judiciary Committee, released a different letter on Friday, sent to him and Ms. Feinstein and signed by 65 women who say they knew Judge Kavanaugh while in high school.

“Through the more than 35 years we have known him, Brett has stood out for his friendship, character and integrity,” the women wrote. “In particular, he has always treated women with decency and respect. That was true when he was in high school, and it has remained true to this day.”

Mr. Grassley was still planning to move ahead with Mr. Kavanaugh’s confirmation. The Judiciary Committee is scheduled to hold a key vote to advance the nomination next Thursday, and Republican leaders hope to hold a final vote of the full Senate before the end of September to allow Mr. Kavanaugh to be seated before the start of the Supreme Court’s fall term next month. Mr. Grassley’s aides said that Mr. Kavanaugh had been the subject of six F.B.I. background checks since 1993, and none had turned up anything like the episode in question.

It was not immediately clear how, if at all, the charges would influence senators who must decide whether to give Mr. Kavanaugh a lifetime appointment to the court. Only a small group of moderate senators remain publicly undecided about their votes, and objections from either one of two undecided Republicans, Senators Susan Collins of Maine and Lisa Murkowski of Alaska, could thwart confirmation.

Ms. Collins spent an hour on the phone with Mr. Kavanaugh on Friday, shortly after details of the letter were first published. The call had been scheduled for days, and neither the White House nor Ms. Collins’s office would disclose what was discussed.

The White House and outside pro-Kavanaugh groups continued to accuse Democrats of playing dirty, withholding mysterious information until the eve of Judge Kavanaugh’s confirmation in a last-ditch effort to derail a nominee they have always opposed.

“I do not intend to allow Judge Kavanaugh’s confirmation to be stalled because of an 11th-hour accusation that Democrats did not see fit to raise for over a month,” Senator Orrin G. Hatch, Republican of Utah, said on Friday. He added: “The claims are wholly unverifiable, and come at the tail end of a process that was already marred by ugly innuendo, dishonesty and the nastiest form of our politics. The American people deserve much better from the Senate as an institution.”