AUGUSTA – Way back when, this was something Susan Collins said she wouldn’t do. And after all these years, Tom Allen looks ready to do something some thought he never would. All of which leaves a large cast waiting in the wings, poised to do whatever.

Speculation abounds over a potential 2008 U.S. Senate election in Maine featuring Collins, a second-term Republican incumbent, against Allen, the sixth-term Democrat representing the state’s 1st Congressional District.

A first hurdle for Collins has been justifying a run at all.

Collins said during her first campaign for the Senate she did not plan to serve more than two terms and thereafter reaffirmed that position when she first sought re-election.

The Bangor Daily News, on Sept. 17, 1996, reported Collins saying: “I want to go to Washington, serve two terms, and then come home.”

Six years later, in a letter dated Sept. 6, 2002, to Carl Lindemann of Portland, Collins wrote: “I am proud of the accomplishments I have made during my first term, and I hope to have the opportunity to serve the people of Maine in the Senate for another six years. I intend to serve only two terms as I indicated in the Sanford forum six years ago.”

But now, heading into a campaign for a third term, Collins says she has had a change of heart. On Oct. 13, 2006, the Sun Journal of Lewiston reported after Collins met with the newspaper’s editorial board that Collins confirmed she would seek re-election in 2008.

“I’ve found that I really underestimated the importance of seniority and how much difference it makes when you are a more senior member,” said Collins, who worked for former U.S. Sen. William Cohen for a dozen years after college.

“At the time, I thought that 12 years, that two terms, would be enough. This was at the height of what I would call the frenzy over term limits,” Collins said.

Allen’s first hurdle, meanwhile, is convincing people that he will take Collins on and persuading potential supporters that he can win.

On WGAN radio in Portland on Friday, Allen continued to stop short of declaring his candidacy.

“I’m seriously considering a run for the Senate,” he said.

Allen added, “I don’t have a date for a decision or an announcement,” and he declined to say why he thinks Collins is vulnerable.

In her last race, Collins soundly defeated an articulate, well-financed Democratic challenger, former state Senate Majority Leader Chellie Pingree of North Haven.

Last week, Pingree said she will be stepping down from the Washington-based job she has held for four years as national president of Common Cause to move back to Maine to assess her political options.

A key focus, Pingree said, would be a 1st District bid.

Pingree may be the best known, but there are a host of other potential 1st District candidates watching to see what Allen does.

On the Democratic side, York County District Attorney Mark Lawrence, the former state Senate president who lost to Republican U.S. Sen. Olympia Snowe in 2000, has announced the formation of an exploratory committee, as has another former state Senate majority leader, Michael Brennan of Portland.

State Sen. Ethan Strimling of Portland is also widely considered to be a potential candidate, state Senate President Beth Edmonds of Freeport and state House Speaker Glenn Cummings of Portland win mention, and Maine Public Utilities Commission Chairman Kurt Adams has long been viewed as a possible congressional hopeful.

At least one relative unknown, lawyer Adam Cote of Portland, who served a year in Iraq with the Maine Army National Guard, is weighing entry.

The Republican list usually starts with former legislator and GOP national committeeman Peter Cianchette of South Portland, who lost to Democrat John Baldacci in Maine’s 2002 gubernatorial election.

Add in former state Sen. Charles Summers of Scarborough, who previously worked for Snowe and for the last two years has been regional administrator of the U.S. Small Business Administration for Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island and Vermont.

Other Republican possibilities include former state Sen. Phil Harriman of Yarmouth, who has been co-hosting a radio talk show with Strimling, and former state Rep. Darlene Curley of Scarborough, who lost to Allen in November.

An intriguing name frequently mentioned is Collins’ chief of staff for 10 years, Steve Abbott.

“I would officially be in the not-ruling-it-out camp,” Abbott joked, also saying he was in the “skeptical” camp about the seat opening up.

A little-known businessman gaining some buzz within Republican Party circles is Dean Scontras of Eliot.

Cianchette, who began a second run for governor in 2005 but then dropped out, hedged in talking about a congressional candidacy last week.

“It’s not something I’ve spent much time thinking about,” he said.

“Personally, I think it would be a huge mistake for Tom Allen to challenge Sen. Collins,” Cianchette said.

But Cianchette suggested he would at least consider making the race if Allen moves on. And Summers all but promised to jump in if Allen declares for the Senate.

“If Tom goes, I’ll be there,” Summers said.