AUGUSTA — Voters across Maine will narrow the field of legislative candidates next month in party primaries designed to produce the best possible slate for November’s general election.

With about 40 primaries on the June 12 ballot — and all 186 legislative seats open in November — Republicans and Democrats say the state is headed for a high-stakes showdown.

“This is the most important election in the history of the Maine Democratic Party,” said Democratic Party Chairman Ben Grant.

That’s because Democrats lost control of the House and Senate for the first time in more than 30 years in 2010 and hope to make a comeback. But Republican Party Chairman Charlie Webster said his party’s field of candidates is stronger, and more mainstream, than those recruited by Democrats.

“We look for barbers, hairdressers and plumbers,” he said. “They’re not Democrats anymore. It’s going to be hard for Democrats to move back to the center.”

Across the state, yard signs are springing up, touting Republicans and Democrats who hope to represent their parties on the Nov. 6 ballot. Notable primary races are shaping up in Old Orchard Beach, Biddeford, Saco, Freeport, Portland, Augusta and Gardiner.

The 35-member Senate appears to be particularly volatile, with 10 senators forced from office by term limits, the most since voters enacted Maine’s four-term limit in 1993. This year, five Republicans and five Democrats cannot run for the Senate again.

Large primary fields in pockets of the state should draw voters’ interest.

In Old Orchard Beach, four Democrats are running for the House District 132 seat, which is being vacated by Rep. George Hogan, a Democrat who is prevented from running again by term limits. The primary winner will face Republican Sharri MacDonald.

In Biddeford, Mayor Alan Casavant, a House member, is being challenged in a primary by state Sen. Nancy Sullivan, who is being forced out of the Senate by term limits. The winner will face Republican William Guay of Kennebunkport.

Biddeford’s two other House seats and the city’s Senate seat have Democratic primaries as well.

And in Augusta, Republicans Michael Hein and Andrew Worcester will square off in the House District 57 primary. Hein is a former employee of the Christian Civic League of Maine. Worcester is a former legislative staffer.

Rep. Maeghan Maloney, D-Augusta, has signed up to run again, although she may be replaced as a candidate because she is running for district attorney.

In Maine, only registered members of the parties can vote in primaries. Voters who are unenrolled now — about 36 percent of Maine’s voters — can join a party any time between now and Election Day, including the day of the election, according to the Secretary of State’s Office.

Assistant House Majority Leader Andre Cushing, R-Hampden, said voters who are interested in the political process can get involved, even if they never have wanted to join any of Maine’s major political parties.

“I believe that’s healthy because you make a conscious decision to select candidates,” he said. “You don’t just vote for a person because they have nice signs, pretty hair or they went to your kid’s ball game.”

Cushing is seeking a Senate seat, and will face James Emerson of Corinna in a primary. He said that knowing a primary is coming makes him pay closer attention to local events, and in this race he has many more towns to cover because he’s seeking to move from the House to the Senate. The winner of his primary will face Democrat Sherman Leighton Jr. of Dexter in November.

The party chairmen, Grant and Webster, say they are hands-off when it comes to primaries, preferring to let candidates compete district by district. The parties provide some support and advice to candidates, but both chairmen say it’s best to let locals decide their nominees, then help the winners focus on November.

Although in other states, and at other levels, primaries can be nasty, Maine legislative primaries tend to stay positive, Grant said. The candidates focus on issues, and do the type of door-to-door campaigning that’s essential to win a local race.

“There’s no doubt in my mind a really well-fought primary is incredibly beneficial to the ultimate winner of that primary,” Grant said. “They have a leg up, going in to the general” election.

That’s because they talk to voters sooner, get their campaign operations going and recruit volunteers. Webster said a well-known community member can also help recruit new party members.

“Most often, people get their sister, brother and neighbor, and get them to join the party,” he said. “They get excited. It’s good.”

Two years ago, Republicans won the trifecta of Maine politics — the House, the Senate and the governor’s office.

Although many expected Republicans to take the Senate, their win in the House took pundits by surprise. Republicans now hold a 77-72-1 majority in the House, with one vacancy, and a 19-15-1 majority in the Senate.

One wrinkle for Republicans this year is the emergence of Ron Paul activists, who took over the party’s state convention last weekend by electing the convention chairman and a majority of the delegates.

Some party insiders say that the process used to select delegates did not follow party rules and that it’s possible the Paul delegates won’t get seated at the national convention this summer in Tampa.

If that happens, Paul’s supporters will likely sit out the November election, which will hurt Republicans running for the Legislature, said Matt McDonald of Belfast, a Paul delegate to the convention.

“The local tea party and Ron Paul people just won’t vote,” he said. “They won’t support local Republican legislators as much as they need to be supported to win. If they don’t seat us, come November, Democrats will seat the House and the Senate.”

Webster isn’t taking that threat lightly. He said he will fight to get the Paul supporters seated at the convention. Although he called them “wingnuts” before the convention, Webster now says he values the energy they bring to the party and hopes they will get involved in legislative elections.

“They will be a huge help to us,” he said. “I’m almost giddy about it.”

It’s unclear at this early stage how much money from national groups will come into the state to help determine the outcome of legislative races.

National groups such as the Democratic Legislative Campaign Committee don’t get involved in primaries, but the group is watching the state to see if its staff or money can make a difference in some districts, said spokesman Dan Roth.

Two years ago, outside money played a significant role in five Senate races. The Republican State Leadership Committee, based in Virginia, spent nearly $400,000 in the last two weeks of the campaign. All five Republican candidates who benefited from the independent expenditure won.

House Minority Leader Emily Cain, D-Orono, said she’s seeing energy among activists that she hasn’t seen in the last 10 years. She’s running for the Senate and does not have a primary opponent. She will face Republican Roderick Hathaway of Veazie in November.

“I think it’s a good problem to have when there are a lot of Democrats motivated to run for office,” she said.

State House Writer Susan Cover can be contacted at 620-7015 or at: scover@mainetoday.com