Republicans seized on signs of movement in their direction yesterday as they unleashed a massive election-eve voter mobilization operation in an effort to stave off potentially substantial losses in the House and preserve at least a slender majority in the Senate.

Democrats answered the Republicans' get-out-the-vote machinery with intensified efforts to contact infrequent and still-undecided voters in a handful of tight Senate races as well as in more than two dozen GOP-held House districts where races were too close to call.

A Pew Research Center poll showed a significant narrowing in the partisan advantage in House races that the Democrats have enjoyed for much of the year, findings that echoed those of a Washington Post-ABC News poll released Saturday showing the Democrats with a six-point edge.

The Pew poll showed that the Democratic advantage had dropped to 47 percent to Republicans' 43 percent among likely voters, down from 50 percent to 39 percent two weeks ago. The poll found a drop in Democratic support among independents, but Pew Director Andrew Kohut said the most significant change over the past two weeks is that Republicans now outnumber Democrats among likely voters.