WASHINGTON  Top supporters of Senator Barack Obama, joined by at least one prominent Democrat yet to endorse a candidate, put pressure on Senator Hillary Rodham Clinton on Sunday to bow out of the presidential race unless she scores clear victories in the crucial big-state primary contests on Tuesday.

“I just think that D-Day is Tuesday,” said Gov. Bill Richardson of New Mexico, a former Democratic presidential candidate who has yet to throw his support behind either candidate.

And two Obama supporters, Senators John Kerry and Dick Durbin, pushed for Mrs. Clinton to withdraw if she does poorly at the polls on Tuesday.

Texas, Ohio, Rhode Island and Vermont hold primary contests that day, and the Clinton campaign, trailing in the delegates needed for nomination and having lost the last 11 straight contests, has acknowledged that the New York senator needs to win at least Ohio or Texas. Both candidates were campaigning Sunday in Ohio.