Obama added superdelegates from Utah, Ohio and Arizona, as well as two from the Virgin Islands who had previously backed Clinton. The additions enabled Obama to surpass Clinton's total for the first time in the campaign. He had picked up nine endorsements Friday.

The milestone is important because Clinton would need to win over the superdelegates by a wide margin to claim the nomination.

They are a group Clinton owned before the first caucus, when she was able to cash in on the popularity of the Clinton brand among the party faithful.

Those party insiders, however, have been steadily streaming to Obama since he started posting wins in early-voting states.

"I always felt that if anybody establishes himself as the clear leader, the superdelegates would fall in line," said Don Fowler, a former chairman of the Democratic National Committee.

"It is perceived that he is the leader," said Fowler, a superdelegate from South Carolina who supports Clinton. "The trickle is going to become an avalanche."

Superdelegates are the party and elected officials who will automatically attend the Democratic National Convention in Denver. They can support whomever they choose, regardless of what happens in the primaries.

Nearly 800 superdelegates will attend the convention. Obama has endorsements from 276, according to the latest tally by the Associated Press. Clinton has 271.5.

ABC News and the New York Times reported separately that Obama had passed Clinton in superdelegates endorsements on Friday. Both of their counts, however, had fewer Clinton superdelegates than the AP count. The Associated Press verifies all superdelegate endorsements included in its count.

Many of the superdelegates who endorsed Obama in the last week said it was time for the party to unite behind him. Obama is coming off a big win in North Carolina's Democratic primary Tuesday. Clinton narrowly won Indiana's primary the same day, but Obama did better than many expected.

Obama has added 21 superdelegates since, and Clinton has had a net increase of two.

Kevin Rodriquez of the Virgin Islands said he switched from Clinton to Obama because he thought Obama had brought energy and excitement to the party.

In all, Obama added five superdelegates late Friday and Saturday. Clinton added one in Massachusetts, but lost the two in the Virgin Islands.

Ohio labor leader Dave Regan, who was selected as a superdelegate yesterday, said Obama was "the candidate that can unite the country and move beyond the divisiveness and gridlock that we have today."

A little more than 200 superdelegates remain undecided, and about 40 others will be named by state parties at state conventions and meetings throughout the spring.

Obama has a 163-delegate lead among the pledged delegates won in primaries and caucuses. That means Clinton would have to generate an identical lead among superdelegates to catch him.

There are 217 pledged delegates at stake in the remaining six primaries. Obama is on track to secure a majority of the pledged delegates on May 20, when Kentucky and Oregon vote.

In the overall race for the nomination, Obama has 1,864.5 delegates and Clinton has 1,697, according to the latest AP tally. Obama is just 160.5 delegates shy of the 2,025 needed to secure the Democratic nomination.

Besides Regan and Rodriquez, Obama added endorsements from Carole Burke of the Virgin Islands, Kristi Cumming of Utah, and Rep. Harry Mitchell of Arizona. Clinton added Arthur Powell, a superdelegate from Massachusetts.

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