Registered Republicans and Democrats will go to the polls across Maine today to elect their parties’ nominees for a U.S. Senate seat and Maine’s two seats in the U.S. House of Representatives.

Voters also will choose the nominees in about 40 legislative districts that have party primaries. And those in some cities and towns will vote on local referendum questions.

Most polling places for today’s primary elections will open at 8 a.m., though a few communities, including Buxton and Lebanon, will open the polls as early as 6 a.m., according to the Secretary of State’s Office. In Portland, South Portland and Westbrook, the polls will be open at 7 a.m.

Polls across the state will close at 8 p.m.

The most high-profile races are for the U.S. Senate seat that will be vacated by Republican Olympia Snowe.

The Republican contenders for the seat are Rick Bennett, Scott D’Amboise, Debra Plowman, Bruce Poliquin, William Schneider and Charlie Summers.

Democrats Cynthia Dill, Matthew Dunlap, Jon Hinck and Benjamin Pollard will appear on their party’s primary ballot for Snowe’s seat.

The only certain thing about the battle for Snowe’s seat is that Angus King’s name will appear on the Nov. 6 ballot. As an independent, the former Maine governor will not compete in a primary.

Republicans will also elect nominees to challenge incumbent Democrats in Maine’s 1st and 2nd Congressional Districts.

Republicans in southern and midcoast Maine must choose between state Sen. Jon Courtney of Springvale and Patrick Calder, a merchant mariner from Portland. The winner will challenge 1st District Rep. Chellie Pingree in the general election Nov. 6.

In central, eastern and northern Maine, Republicans can vote for state Sen. Kevin Raye of Perry or Blaine Richardson of Belfast.

One of them will advance to face 2nd District Rep. Mike Michaud in November.

Pingree and Michaud are both unopposed in the primaries.

To cast ballots in today’s primaries, voters must be registered as Republicans or Democrats.

Election officials expect an unusually low turnout today, based on the number of absentee ballots that had been taken out and cast by the June 5 deadline.

The Secretary of State’s Office said only 4,229 Mainers had requested absentee ballots, compared with 39,946 in June 2010 and 14,430 in June 2008.