PORTLAND — Three signature-gatherers stood outside the First Parish Unitarian Universalist Church on Congress Street and stopped fellow parishioners headed into the Sunday morning service.

They were collecting signatures for U.S. Rep. Chellie Pingree, D-1st District, who has taken out nomination papers for the seat being vacated by Republican U.S. Sen. Olympia Snowe, even though Pingree has no declared her candidacy formally.

“People are eager most of the time,” said Jim Bishop of Saco, who was collecting for state Sen. Phil Bartlett, D-Gorham. Bartlett hopes to run for Pingree’s seat.

Bishop was among the legions of volunteers who fanned out across the state over the weekend to collect enough signatures from registered voters by March 15. They represented almost three dozen candidates who have taken out nomination papers for the U.S. Senate and two House seats, most of them after Snowe turned Maine’s political landscape upside down with her surprise announcement last week that she would not run for a fourth term.

Anywhere there was a crowd, there were signature-gatherers.

They showed up in droves at Portland’s First Friday Art Walk, at the state high school basketball championships at the Cumberland County Civic Center, at concerts and at churches. They got thrown out of the Portland winter farmers’ market at the Maine Irish Heritage Center after annoying the shoppers.

“The art walk was a political mosh pit,” said Rep. Jon Hinck, D-Portland.

Hinck was among those who did a political U-turn last week, shifting his sights from a run for the U.S. Senate to the 1st District House seat. That required Hinck to throw out the hundreds of signatures he already had gathered for the Senate race and start from scratch.

Hinck plans to recycle campaign materials that he had assembled for the Senate race, and he was able to repurpose some political signs left over from his run for the state House of Representatives by cutting and pasting.

Setting out to gather signatures on his home turf in Portland’s heavily Democratic West End on Sunday, Hinck asked supporters to hold on to the U.S. Senate papers, just in case.

“Anything can happen in this race,” Hinck said.

Gathering legitimate signatures isn’t so easy. It entails finding registered voters in the same party who live in the same district as the candidate. Volunteers often carry complicated lists, organized by city and town.

Each gatherer must have the papers notarized, and then municipal clerks must verify the signatures of registered voters in their communities.

The deadline for completing the task is just 10 days away. Republican and Democrat candidates must gather 1,000 valid signatures for the House seats and 2,000 for the Senate seat by March 15. Independents have until June 12.

Bartlett said it takes about an hour to gather 20 signatures, but by Sunday morning he and his volunteers were ahead of schedule.

“The key is to be strategic,” he said.

Retired businessman Mark Gartley, a Republican from Westbrook, spent the weekend organizing his troops in six counties in his bid for the 1st District House seat. Gartley said he met with his signature-gatherers in Westbrook on Sunday morning.

“It is a mad dash until the Ides of March,” Gartley said.

State Sen. Jonathan Courtney, R-Sanford, who took out nomination papers for the 1st District the day after Snowe’s announcement, called the process humbling.

“People are going out in the snow and the rain. It is a real honor,” Courtney said.

While the political landscape remained volatile over the weekend, with some candidates not yet formally announced and other uncertainties, Courtney said he will continue to forge ahead.

Courtney said for him there is no going back, no matter what happens.

“I owe it to them,” he said of his volunteers.