FACTBOX: Democrats expect gains in Congress

(Reuters) - Democrats appear positioned to expand their control of the U.S. Congress in the November elections when Americans will also elect a successor to President George W. Bush. Here are some facts about the congressional contests.

-- Democrats now control both chambers of Congress, the Senate, 51-49, and the House of Representatives, 233-198 with four vacancies. Democrats are expected to pick up at least a handful of seats in both chambers, with a remote shot at reaching a filibuster-proof 60 in the Senate.

-- All 435 House seats are up for election, and so are 35 of the 100 Senate ones. Twenty-three of the Senate races involve seats now held by Republicans, while 12 are held by Democrats.

-- All Senate Democrats up for election are seeking another term. Five Senate Republicans are retiring: Wayne Allard of Colorado, John Warner of Virginia, Chuck Hagel of Nebraska, Pete Domenici of New Mexico and Larry Craig of Idaho.

-- The Republicans' best chance of defeating an incumbent Senate Democrat appears to be Mary Landrieu in Louisiana. Former Democratic Virginia Gov. Mark Warner is heavily favored to win the seat being vacated by retiring Republican Warner.

-- The nonpartisan Cook Political Report lists five Senate races as "tossups," all involving seats held by Republicans. They include the seats of two retiring members, Allard and Domenici, plus three running for re-election -- Alaska's Ted Stevens, Minnesota's Norm Coleman and New Hampshire's John Sununu.

-- Polls show only one in five Americans approves of the Democratic-led Congress. But surveys also find they prefer Democrats over Republicans on a number of issues, such as the Iraq war, economy, health care, education and energy.

(Source: the nonpartisan Cook Political Report, the nonpartisan Rothenberg Political, the Pew Research Center and University of Virginia's Center for Politics.)

(Reporting by Thomas Ferraro; Editing by David Alexander and Peter Cooney)

(For more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at blogs.reuters.com/trail08/)