WASHINGTON — Senator Obama swept the Louisiana primary and caucuses in Nebraska and Washington state last night, slicing into Senator Clinton’s slender delegate lead in their historic race for the Democratic presidential nomination.

The Illinois senator also won caucuses in the Virgin Islands, completing his best night of the campaign.

“Today, voters from the West Coast to the Gulf Coast to the heart of America stood up to say ‘yes we can'” Mr. Obama told a cheering audience of Democrats at a party dinner in Richmond, Va.

He jabbed simultaneously at Mrs. Clinton and Senator McCain, saying the election was a choice between debating the Republican nominee-in-waiting “about who has the most experience in Washington, or debating him about who’s most likely to change Washington. Because that’s a debate we can win.”

Mrs. Clinton preceded Mr. Obama to the podium. She did not refer to the night’s voting, instead turning against Mr. McCain. “We have tried it President Bush’s way,” she said, “and now the Republicans have chosen more of the same.”

She left quickly after her speech, departing before Mr. Obama’s arrival. But his supporters made their presence known, sending up chants of “Obama” from the audience as she made her way offstage.

Mr. Obama’s winning margins ranged from substantial to crushing.

He won roughly two-thirds of the vote in Washington state and Nebraska, and almost 90% in the Virgin Islands.

Nearly complete Louisiana returns showed Mr. Obama with 57% of the vote, to 36% for the former first lady. As in his earlier Southern triumphs in Alabama, Georgia, and South Carolina, Mr. Obama, a black man, rode a wave of African-American support to victory in Louisiana. Mrs. Clinton won the white vote overwhelmingly.

In all, the Democrats scrapped for 161 delegates in the night’s contests.

In incomplete allocations, Mr. Obama won 72, Mrs. Clinton 40.

In overall totals in The Associated Press count, Mrs. Clinton had 1,095 delegates to 1,070 for Mr. Obama, counting so-called superdelegates. They are party leaders not chosen at primaries or caucuses, free to change their minds. A total of 2,025 delegates is required to win the nomination at the national convention in Denver.

Mr. McCain flunked his first ballot tests since becoming the Republican nominee-in-waiting. He lost Kansas caucuses to Michael Huckabee, gaining less than 24% of the vote. Mr. Huckabee, the former Arkansas governor, got nearly 60% of the vote a few hours after saying, “I majored in miracles, and I still believe in them.” He won all 36 delegates at stake.

Mr. Huckabee also won the Louisiana primary, but fell short of 50%, the threshold necessary to pocket the 20 delegates that were available. Instead, they will be awarded at a state convention next weekend.

Mr. McCain won the third Republican race of the night, Washington’s caucuses. None of the state’s delegates will be awarded until next week.

For all his brave talk, Mr. Huckabee was hopelessly behind in the delegate race. Mr. McCain had 719, compared with 234 for Mr. Huckabee and 14 for Rep. Ron Paul of Texas. It takes 1,191 to win the nomination at the national convention.

The Democrats’ race was as close as the Republicans’ was not, a contest between Mr. Obama, hoping to become the first black president, and Mrs. Clinton, campaigning to become the first female commander in chief.

The two rivals contest primaries on Tuesday in Maryland, Virginia, and the District of Columbia, all states where Mr. Obama and his campaign are hopeful of winning.

Preliminary results of a survey of voters leaving their polling places in Louisiana showed that nearly half of those casting ballots were black. As a group, African-Americans have overwhelmingly favored Mr. Obama in earlier primaries, helping him to wins in several Southern states.

Mr. Obama was gaining about 80% of the black votes statewide, while Mrs. Clinton was winning 70% support among whites, the exit poll showed.

One in seven Democratic voters and about one in 10 Republicans said Hurricane Katrina had caused their families severe hardship from which they have not recovered. There was another indication of the impact the storm had on the state. Early results suggested that northern Louisiana accounted for a larger share of the electorate than in the past, presumably the result of the decline in population in the hurricane-battered New Orleans area.

Mr. McCain cleared his path to the party nomination earlier in the week with a string of Super Tuesday victories that drove Mr. Romney from the race. He spent the rest of the week trying to reassure skeptical conservatives, at the same time party leaders quickly closed ranks behind him.

His Kansas defeat aside, Mr. McCain also suffered a symbolic defeat when Mr. Romney edged him out in a straw poll at the Conservative Political Action Conference meeting across town from the White House.

The day’s contests opened a new phase in the Democratic race between Mrs. Clinton and Mr. Obama.

The February 5 Super Tuesday primaries and caucuses in 22 states, which once looked likely to effectively settle the race, instead produced a near-equal delegate split.

That left Mr. Obama and Mrs. Clinton facing the likelihood of a grind-it-out competition lasting into spring — if not to the summer convention itself.

With the night’s events, 29 of the 50 states have selected delegates.

Two more — Michigan and Florida — held renegade primaries and the Democratic National Committee has vowed not to seat any delegates chosen at either of them.

Maine, with 24 delegates, holds caucuses today. Maryland, Virginia, and the District of Columbia and voting by Americans overseas are next, on Tuesday, with 175 combined.

Then follows a brief intermission, followed by a string of election nights, some crowded, some not.

The date of March 4 looms large, 370 delegates in primaries in Ohio, Texas, Rhode Island, and Vermont.

Mississippi is alone in holding a primary one week later, with a relatively small 33 delegates at stake.

Puerto Rico anchors the Democratic calendar, with 55 delegates chosen in caucuses on June 7.

If Super Tuesday failed to settle the campaign, it produced a remarkable surge in fundraising.

Mr. Obama’s aides announced he had raised more than $7 million on line in the two days that followed.

Mrs. Clinton disclosed she had loaned her campaign $5 million late last month in an attempt to counter her rival’s Super Tuesday television advertising. She raised more than $6 million in the two days after the busiest night in primary history.

The television ad wars continued unabated.

Mr. Obama has been airing commercials for more than a week in television markets serving every state that has a contest though February 19.

Mrs. Clinton began airing ads midweek in Washington state, Maine and Nebraska, and added Maryland, Virginia, and the District of Columbia on Friday.

The exit poll was conducted by Edison Media Research and Mitofsky International for The Associated Press and the television networks.