By John Whitesides, Political Correspondent

WASHINGTON, Nov 6 (Reuters) - Democrats took aim at wresting control of the House of Representatives and possibly the Senate from Republicans on Monday, the last day of a bitter U.S. election fight fueled by public discontent with President George W. Bush and the Iraq war.

Both parties fired up get-out-the-vote operations designed to bring core supporters to the polls on Tuesday, and sent out their biggest names to appeal to swing voters who could tip the balance in close races around the country.

Polls showed Democrats could recapture House control for the first time since 1994, but Senate control could hinge on several races that are too close to call. Republicans hoped their vaunted program to identify and turn out voters in the final days of the campaign would limit their losses.

Two polls on Monday showed Democrats with a double-digit advantage when likely voters were asked which party's candidate they would support. The new polls contradicted two surveys released on Sunday that showed Republicans closing the gap on Democrats.

A CNN poll gave Democrats an edge of 20 points, 58 percent to 38 percent, on which party's candidate they would back. A new Fox News poll put the Democratic lead at 13 points.

"Elections tend to tighten as you get closer to the day. But I feel confident about where we are in each of these individual races that we have focused our attention on," Democratic House Leader Nancy Pelosi told an ABC radio affiliate in Portland, Oregon.

"All of this will be turnout. That, of course, is the story of the next 24 hours," said Pelosi, who would likely become the first woman House speaker if Democrats take control, which because of her liberal views is often used as a rallying point for Republicans.

All 435 House seats, 33 Senate seats and 36 governorships are at stake in Tuesday's voting, with Democrats needing to pick up 15 House seats and six Senate seats to seize control of both houses of Congress.