WASHINGTON – Democratic U.S. Rep. Chellie Pingree says she won’t run for the Senate, apparently boosting the independent candidacy of former Gov. Angus King Jr.

Pingree announced Wednesday that she will run for a third term representing Maine’s 1st Congressional District, giving other Democrats a shot at the Senate seat that Republican Olympia Snowe will vacate.

However, Democrats and Republicans face a formidable candidate in King, a social liberal and self-described fiscal conservative who won gubernatorial campaigns in 1994 and 1998. King won re-election with nearly 59 percent of the vote in a five-way race.

Snowe’s decision last week to give up an apparently secure seat has transformed Maine’s Senate race into a key national contest, which could determine whether Democrats keep their majority in the Senate. The race is expected to attract the attention of national party leaders and set new campaign spending records for a federal election in Maine.

Pingree was considered the strongest Democratic candidate for the seat after Rep. Mike Michaud, who represents the 2nd Congressional District, decided a week ago to defend his seat rather than run for the Senate.

Many observers believe King will take many Democratic votes in November, giving the Republican candidate a clean shot at Snowe’s seat.

In an interview Wednesday, Pingree said, “We have seen three-way contests before become very complex (in Maine) and I didn’t want to take the chance that my entering the race would make it more likely for a Republican to be the next senator from the state of Maine.”

King said in a prepared statement that he was surprised to learn of Pingree’s decision, but added, “This is a personal relief to me because I wasn’t looking forward to running against a friend.”

Pingree’s decision leaves another former governor, John Baldacci, as the most noteworthy prospective Democratic candidate for Snowe’s seat. Dan Cashman, a Baldacci spokesman, said Wednesday that Baldacci is “still weighing his options for a potential run and will have an announcement one way or the other when he is ready.”

Party candidates have until March 15 to submit at least 2,000 signatures to get on the June 12 primary ballot.

Baldacci has been working at the Pentagon, in a contract job studying military health care reform issues. That job ends this month, Cashman said, “and any decision he makes regarding a potential Senate run is independent from his position at the Pentagon.”

Former Maine Secretary of State Matthew Dunlap, a Democrat, says he is running for the Senate. And Democratic state Sen. Cynthia Dill of Cape Elizabeth, who shifted from a Senate candidate to a House candidate when it appeared that Pingree might run for the Senate, said Wednesday that she is now back in the Senate race.

State Rep. Jon Hinck of Portland, another Democratic Senate candidate who thought about running for the House, said Wednesday night that he now is back as a Senate candidate.

The Republican field now has about a dozen declared candidates. One of them, state Sen. Debra Plowman of Hampden, said that as the GOP nominee, she would have had a better chance of winning a three-way race with Pingree and King competing for Democrats’ votes.

“I would have preferred that she stay in the race, to tell you the truth,” said Plowman, the assistant state Senate majority leader.

Several of her potential primary opponents are better known statewide, including former Maine Senate President Rick Bennett, Secretary of State Charlie Summers, Attorney General William Schneider and state Treasurer Bruce Poliquin.

The GOP field also includes Scott D’Amboise, a businessman from Lisbon Falls who is affiliated with the tea party and began running for the nomination last year.

Summers said he is committed to running for the Senate and is now focused on gathering 2,000 certified signatures by the March 15 deadline. “I believe I will run, absolutely,” he said.

Bennett, who lives in Oxford and is chief executive officer of a Portland investment research firm, said he is seriously considering running.

Pingree’s decision not to run for the Senate seat will likely prompt many, if not all, of the 12 Democrats who have expressed interest in succeeding her to drop out of the race. Pingree is seen as the favorite as an incumbent in the Democratic-leaning district.

However, a potential opponent, state Senate Majority Leader Jonathan Courtney, R-Springvale, said Congress is extremely unpopular and people are looking for a change.

Courtney, who owns a dry cleaning business in Sanford, said Pingree, who is married to S. Donald Sussman, a wealthy hedge fund manager, is out of touch with ordinary people.

“We need someone who listens to them and knows what it means to struggle to earn a living,” he said.

Sussman, a frequent Democratic donor, is buying a 5 percent equity stake in MaineToday Media, which owns The Portland Press Herald/Maine Sunday Telegram, the Kennebec Journal in Augusta, the Morning Sentinel in Waterville and other media outlets.

Courtney began collecting signatures last week. He said Pingree’s decision to defend her seat won’t change his mind about running for Congress.

Other GOP candidates in the 1st District are Markham Gartley, a former secretary of state, and four newcomers with little or no political experience.

King said in an interview Tuesday with The Portland Press Herald that he would wait until he got to Washington to decide whether to caucus with Democrats or Republicans, basing his decision on “what’s most effective for Maine,” not an ideological preference for either party.

King declared his candidacy Monday. As an independent, he has until June 1 to submit at least 4,000 signatures to get on November’s general election ballot.

Staff Writer Tom Bell contributed to this report.

MaineToday Media Washington Bureau Chief Jonathan Riskind can be contacted at 791-6280 or:

jriskind@mainetoday.com

Twitter.com/MaineTodayDCD