Two weeks before Election Day, the competitive advantage that the Democrats have held over the Republicans in the battle for seats in Congress has grown. Over the past week, CQ Politics changed its ratings on 29 House races — all but one of which signified stronger chances for the Democratic candidates. Most of these changes were outlined in stories published on Friday and on Saturday.

While there were no new rating changes in the Senate races, the Democrats continued to run serious campaigns for 12 Republican-held seats, while only one Democratic seat is the subject of a Republican takeover bid that looks the least bit competitive.

Yet CQ Politics’ Balance of Power scorecards for the Senate and the House show that the degree to which the Democrats will pad their current majorities in both chambers continues to be uncertain. That is because many of the contests are rated No Clear Favorite, meaning that they still appear too close to call.

The Senate scorecard shows the Democrats likely to have at least 56 seats after the election, based on CQ Politics’ current ratings. That figure — which includes independents Bernard Sanders of Vermont and Joseph I. Lieberman of Connecticut, who caucus with the Democrats for organizational purposes — reflects five contests in which the Democrats are slightly to strongly favored to take over Republican-held seats: the open-seat races in Virginia, New Mexico and Colorado and the challenges to incumbents Ted Stevens of Alaska and John E. Sununu of New Hampshire.

If the Democrats are to meet or exceed their oft-stated goal of claiming 60 or more seats, for a so-called “filibuster-proof majority,” they would have to win all five of those races, and either sweep the four races for Republican seats currently rated as No Clear Favorite, or pick off one or more of the three seats in the competitive races rated Leans Republican.

The most recent independent polls suggest a Democratic sweep is not an outlandish proposition, though.

• In Oregon, where Republican Sen. Gordon Smith is seeking a third term, polls by Survey USA and Research 2000 showed Democrat Jeff Merkley, the state House Speaker, with leads of 5 and 6 percentage points, respectively, while the most recent Rasmussen organization’s poll showed the race tied.

• In the high-profile Minnesota race, first-term Republican incumbent Norm Coleman and Democrat Al Franken, a well-known entertainer, were in statistical ties in polls taken by Quinnipiac University, Research 2000 and Survey USA, with both candidates hovering around the 40 percent mark. The only constant being the 18 percent pulled in each poll by third-party candidate Dean Barkley.

• In North Carolina, first-term Republican Sen. Elizabeth Dole trailed Democratic state Sen. Kay Hagan by 4 percentage points in a Research 2000 poll.

• In Mississippi’s Senate special election, appointed Republican Sen. Roger Wicker led Democratic former Gov. Ronnie Musgrove by a statistical insignificant 1-point margin in a Research 2000 poll.

Democrats are hoping for even bigger upsets. Republicans Mitch McConnell of Kentucky, challenged by Democratic businessman Bruce Lunsford, and Saxby Chambliss of Georgia, opposed by Democratic former state Rep. Jim Martin, hung on to small but uncertain leads in their most recent polls, while Susan Collins , Maine’s popular two-term senator, maintained a wider lead over Democratic Rep. Tom Allen . The only Democrat facing a threatening challenge, two-term Louisiana Sen. Mary L. Landrieu , appears in fairly good shape in her race against Republican state Treasurer John Kennedy, now rated Leans Democratic.

The House Balance of Power scorecard masks somewhat the Democrats’ potential for big gains. With two weeks left to go, there are 235 races rated Leans Democratic (17), Democrat Favored (16) or Safe Democratic (202), which actually is one seat fewer than the party currently holds. But the Republicans currently are slightly to strongly favored for just 176 seats — 23 fewer than they now have — with 25 rated Leans Republican, 25 rated Republican Favored and 126 rated Safe Republican.

This past week brought one of the few clear gains this fall for the Republicans. The rating on the race in Florida’s 16th District, where freshman Democrat Tim Mahoney is the incumbent, was changed from No Clear Favorite to Leans Republican, making it the only Democratic seat currently deemed likely to fall to the Republicans. Mahoney, who won the seat in 2006 largely because of the scandal involving resigned Republican Rep. Mark Foley’s inappropriate advances on underage male pages, was hit with a sex scandal of his own, admitting to multiple extramarital relationships, including one with a woman staffer whom he paid a large sum of money to avoid a sexual harassment lawsuit.