WASHINGTON — The Senate Judiciary Committee and lawyers for the woman who has accused Judge Brett M. Kavanaugh of sexually assaulting her decades ago reached a tentative agreement on Saturday for her to publicly testify on Thursday, an apparent breakthrough that could alter the course of a bitter confirmation fight.

After a brief call late on Saturday, the woman’s lawyers and aides to Senator Charles E. Grassley of Iowa, the Republican chairman of the Judiciary Committee, planned to talk again Sunday morning to continue the halting negotiations over the conditions of the testimony, according to three people familiar with the call. Aides to Senator Dianne Feinstein of California, the committee’s top Democrat, were also involved.

But in a possible setback for the woman, Christine Blasey Ford, Republicans on the committee received a statement on Saturday that seemed to eliminate any chance of corroboration of Dr. Blasey’s account by anyone who attended the high school party where she says she was assaulted.

A woman named Leland Keyser — who is believed to have been identified by Dr. Blasey as one of the five people at the party — told the committee through a lawyer that she “does not know Mr. Kavanaugh and she has no recollection of ever being at a party or gathering where he was present, with, or without, Dr. Ford.” Two men said to have been at the party, Mark Judge and Patrick Smyth, have also told the committee that they have no recollection of the events.