PORTLAND, Ore.  “I talked to Senator Clinton last night,” Gov. Bill Richardson of New Mexico said on Friday, describing the tense telephone call in which he informed Senator Hillary Rodham Clinton that, despite two months of personal entreaties by her and her husband, he would be endorsing Senator Barack Obama for president.

“Let me tell you: we’ve had better conversations,” Mr. Richardson said.

The decision by Mr. Richardson, who ended his own presidential campaign on Jan. 10, to support Mr. Obama was a belt of bad news for Mrs. Clinton. It was a stinging rejection of her candidacy by a man who had served in two senior positions in President Bill Clinton’s administration, and who is one of the nation’s most prominent elected Hispanics. Mr. Richardson came back from vacation to announce his endorsement at a moment when Mrs. Clinton’s hopes of winning the Democratic nomination seem to be dimming.

But potentially more troublesome for Mrs. Clinton was what Mr. Richardson said in announcing his decision. He criticized the tenor of Mrs. Clinton’s campaign. He praised Mr. Obama for the speech he gave in response to the furor over racially incendiary remarks delivered by Mr. Obama’s former pastor, the Rev. Jeremiah A. Wright Jr.

And he came close to doing what Mrs. Clinton’s advisers have increasingly feared some big-name Democrat would do as the battle for the nomination drags on: Urge Mrs. Clinton to step aside in the interest of party unity.