Barack Obama received a significant boost to his presidential campaign yesterday when he received the coveted endorsement of Bill Richardson, a high-profile superdelegate and former member of Bill Clinton's Cabinet.

The backing of Mr Richardson, the Hispanic governor of New Mexico who dropped out of the Democratic presidential race in January, came after a bad week for Mr Obama, who has been damaged by incendiary remarks made by his former pastor.

Mr Richardson, who served as Energy Secretary and UN ambassador under Mr Clinton and has close ties to him and his wife, had been relentlessly courted by the former president. He even flew to New Mexico to watch last month's Super Bowl game with the New Mexico governor.

A clearly emotional Mr Richardson, standing next to Mr Obama at a huge rally in Oregon, said: "Your candidacy is a one-in-a lifetime opportunity for our nation and you are a once-in-a-lifetime leader."

He praised the Clintons, but declared: 'It is time for the Democrats to stop fighting among ourselves and prepare for the tough fight against John McCain."

He also referred to Mr Obama's speech this week on race, in which he tried to defuse the controversy over the inflammatory comments of the Reverend Jeremiah Wright, as the words of a "courageous, thoughtful and inspiring leader".

Mr Obama has seen Mrs Clinton overtake him in national opinion polls since the Wright controversy, but their nomination race is now focused almost solely on wooing the party's so-called superdelegates, the congressman, senators, governors and senior officials who will likely determine the race.

Mr Richardson's backing is a major boost for Mr Obama. It comes after Nancy Pelosi, the House Speaker, appeared to back Mr Obama on Sunday, when she said superdelegates should get behind the candidate who emerges in June with the most elected delegates from the primary and caucus process. Mr Obama has an almost impregnable lead among pledged delegates.

Joe Trippi, the former campaign manager for John Edwards, who dropped out of the race in January, said Mr Richardson "may open the door for other superdelegates to start moving to Obama."

In a clumsy move, the Obama campaign circulated a picture of Mr Clinton meeting Mr Wright in the White House in 1998, during a gathering of ministers at the height of the Monica Lewinsky scandal. The Clinton campaign called it "pathetic".

Meanwhile, the fallout from the Wright controversy continued to dog Mr Obama. In his speech on Tuesday he cited racially insensitive comments made by his white grandmother. In an interview on Wednesday, he called her a "typical white person", a comment that drew further criticism.

Mr Obama and Mrs Clinton spent record sums last month, according to new figures. Mr Obama raised over $55 million, and spent nearly $43 million - about $1.5 million a day. Mrs Clinton raised $34.5 million, and spent nearly $32 million.

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