PORTLAND – U.S. Rep. Tom Allen threw his support behind Sen. Barack Obama as the Democratic presidential nominee and said Monday it’s time for the Democratic primary campaign to come to a “graceful end.”

Allen, a superdelegate to this summer’s Democratic national convention, said he believes Obama and Sen. Hillary Rodham Clinton are both “supremely qualified” to be president.

But most of the nation’s primary and caucus voters have spoken, and the Democratic Party should now focus on unifying and winning the White House and Congress come November, Allen said at a news conference.

“I’ve watched independents and Democrats and even a lot of Republicans in Maine enthusiastically support Obama because they believe he can and will put America back on track,” he said. “I believe the process of reconciliation, the process of unifying this party, should begin sooner rather than later. It should begin in May and not in June.”

Allen is the latest superdelegate to pledge support for Obama, the front-runner in the Democratic presidential campaign.

The Illinois senator has a lead in pledged delegates, and now has the lead among superdelegates, the nearly 800 party and elected officials who are free to support whomever they choose at the Democratic National Convention in August in Denver.

Obama added five superdelegates to his side over the weekend, and coming into Monday had endorsements from 276 superdelegates to 271.5 for Clinton, according to the latest tally from The Associated Press.

Maine Democrats send 32 delegates to the national convention, including eight superdelegates. Of the 24 pledged delegates, 15 are projected to support Obama and nine are pledged to Clinton.

Among superdelegates, Allen is the third to pledge to Obama, while Clinton has the backing of Gov. John Baldacci. Four remain uncommitted.

Allen has been friends with Hillary Clinton’s husband, former President Bill Clinton, since they were Rhodes scholars together when they were in their early 20s. He has known Hillary since 1991, he said.

Allen said he had placed calls to both Clintons but hadn’t spoken to either about his decision to support Obama.

“Personally this is a difficult decision for me,” Allen said. “But I believe it’s in the best interest of the country.”

Allen, a six-term congressman, is running for the Senate against Republican incumbent Susan Collins.

While announcing his support for Obama, he released a prepared statement in which Obama gives his support to Allen.