WASHINGTON (AP) - Barack Obama's wave of superdelegate endorsements puts him within reach of the Democratic presidential nomination by the end of the primary season on June 3 - even if he loses half of the remaining six contests.

The Illinois senator has picked up 26 superdelegates in the past week. At that pace, he will reach the number of delegates needed to clinch the nomination - 2,025 - in the next three weeks, when delegates from the remaining primaries are included.

Sen. Hillary Rodham Clinton's best chance to slow Obama is to move the goal posts. She will get that chance May 31 when the Democratic National Committee's rules panel considers proposals to seat the delegates that had been stripped from Florida and Michigan. Those two states violated national party rules by holding their primaries in January and lost their delegates.

"Michigan and Florida are key to it," Howard Wolfson, Clinton's communications director, said Monday.

Obama picked up four superdelegates Monday, including Sen. Daniel Akaka of Hawaii and Rep. Tom Allen of Maine.

Allen, a six-term congressman who is running for the Senate, said the time has come for a "graceful end" to the nomination fight.

"I believe the process of reconciliation, the process of unifying this party, should begin sooner rather than later," Allen said. "It should begin in May and not in June."

Obama has 1,871.5 delegates, including endorsements from party and elected officials known as superdelegates. Clinton has 1,697, according to the latest tally by The Associated Press. That leaves Obama just 153.5 delegates short of the number needed to win the nomination at the party's national convention this August in Denver.

There are 217 delegates at stake in the six remaining primaries, in West Virginia, Kentucky, Oregon, Puerto Rico, Montana and South Dakota. Even if Clinton wins most of those delegates, Obama could reach the magic number by the time South Dakota and Montana vote on June 3.

Obama has been careful not to declare himself the nominee prematurely, even as his campaign focuses increasingly on Republican Sen. John McCain. Clinton's campaign, meanwhile, has outlined a strategy for winning the nomination that extends beyond the end of the primaries.

The battle might not last that long.

For Clinton to have a shot, she needs several things to fall her way, including the remaining superdelegates. Obama has claimed more than 80 percent of the superdelegates since Super Tuesday on Feb. 5. He now leads in states won, pledged delegates won in primaries and caucuses and superdelegate endorsements.

He erased her longtime advantage in superdelegates this weekend and now leads 281-271.5. Some 200 undecided superdelegates remain, with an additional 42 still to be selected at state party conventions and meetings throughout the spring. Superdelegates are party leaders who attend the convention as delegates by virtue of their positions, and are not selected in primaries and caucuses.

Clinton desperately needs to have the delegates from Michigan and Florida seated in a way that greatly benefits her.

"It would be helpful," Wolfson acknowledged.

The Democratic National Committee's rules and bylaws committee voted to strip all the delegates from Florida and Michigan because they violated party rules by holding primaries before Feb. 5. The same panel will consider reinstating them.

Under the votes cast in January, Clinton would have won most of the delegates in both states. However, neither candidate campaigned in either state and Obama had his name removed from the ballot in Michigan.

Reinstating all the delegates and superdelegates would increase the number needed to claim the nomination to 2,209, perhaps extending the campaign. But even under the best scenario for Clinton, Obama would still be left with a lead of about 100 delegates, with fewer than 300 superdelegates left to be claimed.

"We need to do well everywhere," Wolfson said. "Our hope is that superdelegates will look at the results in some of these states and recognize that Senator Clinton would be the best nominee against John McCain."

Associated Press Writer Clarke Canfield in Portland, Maine, contributed to this report.