Obama won at least 65 delegates in Tuesday's primaries, with 70 still to be awarded. Clinton won at least 33.
Obama won 52 of Washington state's 78 delegates, according to caucus results released by the state party Tuesday night. Clinton won 26.
In the overall race for the nomination, Obama had 1,223, including separately chosen party and elected officials known as superdelegates. Clinton had 1,198.
It will take 2,025 delegates to secure the Democratic nomination.
Barack Obama says his latest trio of Democratic primary victories is part of a new majority drawing people from every region and every group in the country behind his call for change.
The Illinois senator won presidential primaries Tuesday in Virginia, Maryland and the District of Columbia. He flew to Madison, Wis., where he celebrated his triumphs at a heartland rally. He relished the symbolism of winning in the nation's capital, even though the outcome of that race was never in doubt.
Obama told cheering supporters in Wisconsin that although he won in Washington, D.C., his movement won't stop until there's change in Washington, D.C.
Obama was campaigning in Wisconsin for its Feb. 19 primary.
The Associated Press made its call based on surveys of voters as they left the polls.
The interviews with voters showed blacks accounted for nearly one-third of the ballots cast in Virginia, and Obama's share approached 90 percent. He and Clinton split the white vote.
In all, there were 168 delegates at stake in the three Democratic primaries.
Clinton began the night with 1,147 delegates, to 1,124 for Obama. Both are far from the 2,025 needed to win the nomination at the Democratic National Convention this summer.
The Democratic race was the definition of unsettled, with Clinton on the verge of surrendering her long-held lead in delegates, having shed her campaign manager and loaned her campaign $5 million in recent days, and facing defeats next week in Wisconsin and Hawaii.
She hopes to respond with victories in Texas and Ohio on March 4, states where both candidates have already begun television advertising.
Since last week's Super Tuesday contests in 22 states, Obama has won a primary in Louisiana as well as caucuses in Nebraska, Washington and Maine, all of them by large margins.
Obama has campaigned before huge crowds in recent days, and far outspent his rival on TV advertising in the states participating in the regional primary in Maryland, Virginia and the District of Columbia.
He began airing commercials in the region more than a week ago, and spent an estimated $1.4 million. Clinton began hers last Friday, at a cost estimated at $210,000.
With Clinton facing a series of possible defeats, and Obama riding a wave of momentum, the two camps debated which contender is more likely to defeat McCain in the general election.
An Associated Press-Ipsos poll found Obama with a narrow lead over the Arizona senator in a potential match-up, and Clinton running about even.
"We bring in voters who haven't given Democrats a chance" in the past, said Obama pollster Cornell Belcher, citing support from independents.
Mark Penn, Clinton's chief strategist, countered that she holds appeal for women voters and Hispanics. "Hillary Clinton has a coalition of voters well-suited to winning the general election," he said.
A note on calculating delegates:
The AP tracks the delegate races by projecting the number of national convention delegates won by candidates in each presidential primary or caucus, based on state and national party rules, and by interviewing unpledged delegates to obtain their preferences.
In some states, like Iowa and Nevada, local precinct caucuses are the first stage in the allocation process. The AP uses preferences expressed in those caucuses to project the number of national convention delegates each candidate will have when they are chosen at county, congressional district or state conventions.