(CBS/AP) Barack Obama has taken a slim lead over Hillary Rodham Clinton in the number of Democratic superdelegates Saturday, and won fresh labor backing as elements of the party began coalescing around the Illinois senator for the fall campaign.

According to the latest CBS News tally, Obama now has 274 superdelegates who have pledged their support compared to Clinton's 271.

Overall, Obama now has 1,860 delegates and Clinton has 1,690. (Click here for the full CBS News state-by-state tally.)

Obama added four superdelegates today, when the Utah Democratic Party selected superdelegate add-on Kristi Cumming who (the UT Democratic Party confirmed) is backing Obama. The Illinois Senator also picked up two superdelegates from the Virgin Islands, once of whom had been pledged to Clinton and another from Ohio.

Clinton made up for that loss by acquiring the support of a superdelegate from Massachusetts.

“While the count can change, this is an important symbolic moment,” said CBSNews.com senior political editor Vaughn Ververs. “Obama now leads the Democratic race in every metric - pledged delegates, the popular vote and, now, superdelegates. It takes away one more of Clinton’s dwindling claims on the nomination and solidifies his position as the prohibitive front-runner.”

On Friday Obama picked up the support of 7 superdelegates: Rep Mazie Hirono of Hawaii, Rep. Donald Payne of New Jersey, Rep. Pete Defazio of Oregon, Laurie Weahkee of New Mexico, Wilber Lee Jeffcoat of South Carolina, Ed Espinoza of California and John Gage of Maryland.

Payne, a member of the Congressional Black Caucus, had been a Clinton supporter.

"After careful consideration, I have reached the conclusion that Barack Obama can best bring about the change that our country so desperately wants and needs," said Payne, who in a statement said that Clinton is a good friend and he still holds her in high regard.

Payne is one of at least 10 superdelegates who have switched allegiances from Clinton to Obama. None have publicly switched the other way.

Gage is president of the American Federation of Government Employees, a union of 600,000 members who work in the federal and Washington, D.C., governments. The union also announced its support for Obama on Friday.

"Our people, I think, recognize the enthusiasm and vitality behind Senator Obama's campaign," Gage said in a statement.

Obama, who won a convincing victory in the North Carolina primary and lost Indiana narrowly on Tuesday, has been steadily gaining strength in the days since.

"I'm gratified that we've got some superdelegates who are coming our way. And I think we've got a strong case to make that I will be a nominee that can pull the party together and take on John McCain. Our focus has always been on the pledged delegates and just getting the American people to vote for us. And we think that ultimately that should be the strongest measure of who's the nominee," Obama told reporters in Woodburn, Ore.

Clinton also gained a superdelegate on Friday, Rep. Chris Carney of Pennsylvania. His congressional district voted overwhelmingly for the former first lady in the Pennsylvania primary on April 22.

Superdelegates are party leaders who attend the convention delegates by virtue of their positions, and are not selected in primaries and caucuses.

In an interview with National Public Radio, former candidate John Edwards said Clinton has made a compelling case for her candidacy, but "I think it's very hard for her now to make a compelling case for the math. I mean, I think that's the reality of what she's faced with. She knows that. ... It's just very hard to see how the math works."

Edwards has not endorsed either candidate since he dropped out of the race in January.

Both candidates have courted superdelegates in recent days in private meetings at party headquarters not far from the Capitol.

Clinton has shown no signs she is ready to quit the race. She is heavily favored to win Tuesday's primary in West Virginia, and is in the midst of a two-day swing through several other states with upcoming elections.

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