WASHINGTON -- The presidential race isn’t the only unpredictable war for control of Washington this year. Keep an eye on the U.S. Senate.

Expectations of a Republican takeover, which were widespread over the summer, are fading. Now the Democrats could retain their majority. Either way, it’s close, and no one can safely say which party will have a Senate majority after the Nov. 6 elections.

Among the changes in the landscape: President Barack Obama has an edge over Republican Mitt Romney in national polls as well as in key swing states such as Virginia and Nevada, suggesting that Democrats might turn out in bigger numbers and also vote for Democratic Senate candidates.

Another: The once-vulnerable seat held by Sen. Claire McCaskill of Missouri now appears safely Democratic since the Republican nominee, U.S. Rep. Todd Akin, said this summer that women rarely got pregnant in cases of “legitimate rape.”

Republicans need a net gain of four seats to take control of the Senate if Obama wins, three if Romney is elected — since his vice president would break a tie. Democrats now control 53 seats, but 23 of them are at stake. Republicans need to defend only 10.

Adding to the uncertainty: 2012 isn’t shaping up as a “wave election,” when voters routinely sweep candidates of one political party out of office.

Instead, “there’s hand-to-hand combat, state by state,” said Nathan Gonzales, a political analyst at the nonpartisan Rothenberg Political Report.

He and other experts advise watching 10 races. Five are genuine tossups, too close to call and likely to hinge on the right last-minute ads or debate quirks, or whether partisans do turn out in big numbers for Romney or Obama.

Rothenberg and The Cook Political Report, a nonpartisan firm that follows campaigns closely, agree that at the moment, Montana, North Dakota and Virginia, now held by Democrats, and Massachusetts and Nevada, now Republican seats, are too close to call.

A second group of contests have potential to become volatile: Hawaii, Wisconsin and Missouri, all now Democratic seats, and Indiana, now held by a Republican. Also in the mix is the Connecticut seat held by retiring Sen. Joe Lieberman, an independent who caucuses with Democrats.

The dominant issue in all these races is the economy and who can best fix it. One factor that doesn’t appear to be driving Senate campaigns is the public’s disdain for Congress. Gallup found earlier this month that Congress’ approval rating had sunk to 13 percent, its lowest figure this late in an election year since such polls began in 1974.

With Democrats now in charge of the White House and Senate, and Republicans holding a majority in the House of Representatives, voters tend to see Washington inertia as the result of gridlock, not ineptitude. Voters figure that if only they can elect more people from the party they prefer, Washington will work.

“Everyone thinks their party can do better,” said David Damore, an associate professor of political science at the University of Nevada Las Vegas.

Here are the races to watch closely:

Montana

Two candidates who’ve successfully run statewide, freshman incumbent Democratic Sen. Jon Tester, and Republican Denny Rehberg, the state’s six-term at-large congressman, are in a slugfest that’s impossible to call. The Cook Political Report’s Jennifer Duffy termed this race “a marathon on a treadmill.”