WASHINGTON >> With nearly a dozen Democratic-held Senate seats in play, Republicans expect to cut deeply into Democrats’ majority but may fall short of winning control.

If Republicans win 10 of the dozen Democratic seats without losing any of their own, they will be the Senate’s new majority party. A nine-seat loss would produce a 50-50 tie that Vice President Joe Biden, the Senate’s official president, would break in the Democrats’ favor.

Compelling story lines abound:

>> The Senate’s most powerful member, Majority Leader Harry Reid of Nevada, could lose to a political outsider, tea party champion Sharron Angle.

>> A tempestuous three-way race in Alaska could allow Democrat Scott McAdams to win a once-hopeless race for GOP Sen. Lisa Murkowski’s seat. Murkowski is running a rare write-in campaign after losing the Republican primary to another tea partier, Joe Miller.

>> Still another tea partier, Christine O’Donnell of Delaware, might reap a boatload of blame if she loses to Democrat Chris Coons, as expected, and Republicans fall one seat short of a Senate majority. Rep. Mike Castle, whom O’Donnell beat in the GOP primary, had been heavily favored to beat Coons in the general election.

Republicans seem almost certain to pick up Senate seats in North Dakota and Indiana — where Democrats are retiring — and in Arkansas, where two-term Sen. Blanche Lincoln has trailed Republican Rep. John Boozman in polls.

Another Democrat, Sen. Russ Feingold of Wisconsin, is in severe danger of losing to GOP newcomer Ron Johnson.

Arguably the four closest races are for Democratic-held seats in Nevada, Colorado, Illinois and Pennsylvania.

An Angle win over Reid would mark a spectacular achievement for tea partiers, the libertarian-leaning movement that emerged last year and maintains an uneasy relationship with the Republican Party.

Republican Ken Buck of Colorado, another tea party favorite, has run a neck-and-neck race against Democratic Sen. Michael Bennet, appointed to fill the remaining term of Interior Secretary Ken Salazar but running a strong campaign in his first-ever race.

The race to fill the open Illinois Senate seat once held by President Barack Obama pits Republican Mark Kirk, a five-term House member, against state treasurer Alexi Giannoulias.

In Pennsylvania, Democratic Rep. Joe Sestak beat Republican-turned-Democratic Sen. Arlen Specter in the Senate primary, but he has struggled against GOP nominee Pat Toomey.

West Virginia Democrats predict Gov. Joe Manchin will beat Republican John Raese for the seat long held by the late Robert C. Byrd, but the contest appears tight.

If Republicans win all those close races, and avoid a McAdams win in Alaska, they will have to oust Sen. Patty Murray of Washington or Barbara Boxer of California to claim the Senate majority. Both incumbents were slightly favored in the final days, with Boxer seen as slightly stronger than Murray.

Democrats technically hold 57 Senate seats, but two independent senators caucus with the party.