COLUMBUS, Ohio — The man who served as national manager of President Clinton’s 1992 campaign plans to endorse Senator Obama, an aide to Mr. Obama said today.

Mr. Obama’s campaign planned a 1 p.m. conference call today to announce the endorsement by David Wilhelm, who later became chairman of the Democratic National Committee, according to an aide who spoke on condition of anonymity because the announcement would be made public later in the day.

Mr. Wilhelm planned to tell reporters that Mr. Obama can build a coalition of Democrats, independents, and Republicans needed to win the general election.

Mr. Wilhelm is a superdelegate who was previously uncommitted in the race. His endorsement helps Mr. Obama in the race for delegates, in which he pulled ahead after yesterday’s sweeps of primaries in Virginia, Maryland, and the District of Columbia. Senator Clinton remains considerably ahead in superdelegates, which are party officials, elected officials, and others who can vote however they choose at the nominating convention.

If the race for pledged delegates based on outcomes in caucuses and primaries across the country remains tight, superdelegates could decide the nomination.

Mr. Obama leads the delegate race with 1,224 to 1,198 to Mrs. Clinton, according to the latest count by The Associated Press.