WASHINGTON -- Worsening disapproval scores for the Democrats in Congress have spawned party-wide fears that voter alienation could give Republicans a chance to make a comeback in 2008.

The Democrats' tumbling voter-approval numbers haven't drawn much attention on the nightly news shows, but they have stirred warnings in the party's inner circles and raised hopes among GOP strategists for the first time since last year's election rout drove them from power.

A string of independent polls in the past two weeks tells the story: -- A nationwide Pew Research Center poll found that barely 33 percent of Americans surveyed "approve of the job performance of the Democratic Congress." Equally disturbing to Democrats, their party's leadership "can claim just a 62 percent approval score among Democrats."

-- The Gallup Poll reported "that 55 percent of Americans disapprove of Democrats in Congress."

These and other internal polls have sent tremors through Democratic ranks, and campaign strategists are warning their party to start taking them seriously before it's too late.

"Democrats should not be for complacency in the face of lost trust in Congress and perceptions that the new Congress is not effective or honoring its pledges," party advisers James Carville and Stan Greenberg warned in a midyear strategy memo to Democratic leaders.

Republican numbers are not any better. But the "Democrats should not relish an increasingly alienated electorate on any grounds; increasing alienation from both parties can drive down turnout and create protest voters looking for other vehicles for change," the two strategists said.

That points to fear of a third-party presidential candidacy that could hurt Democratic chances to win back the White House and undermine their tenuous hold on Congress -- a fear no longer dismissed by party leaders.

The testy political climate can hurt both parties, they said. "The mood of the country grows uglier ... and the Democratic Congress and leaders have lost some of the earlier glow; a 55 percent majority believes Democrats have not made progress on their election pledges," the memo said.

Up until now, Democrats have blamed their declining poll ratings on the party's failure to legislate a troop-withdrawal deadline in the Iraq war. "The Democrats are frustrated. They want the war to end quicker than it appears it will," a senior party official told me. But the finer polling data and reports from the party's grassroots base suggest that voter angst runs deeper than that. They see a party engaged in vengeful inquisitions against the Bush administration that have yielded no evidence of wrongdoing, while poisoning the political atmosphere and sinking Congress deeper into legislative gridlock.

A wave of Democratic investigations "creates the perception they are launching witch-hunts," said David Wasserman, House elections analyst at the Cook Political Report.

A Greenberg poll accompanying the Carville-Greenberg memo noted ominously "that, faced with the current gridlock, 12 percent want to vote for an independent candidate for president or Congress, a fairly impressive base for an independent candidacy." Worse, they added, "almost a third of independents are ready to respond in this way. The situation in Washington does have consequences, which is why Democrats have an obligation to address the mood" that has alienated voters.

The Democrats' mediocre approval ratings and restive political base have clearly buoyed GOP spirits, particularly at the National Republican Congressional Committee (NRCC).

"Such widespread dissatisfaction is creating a palpable sense of panic among Democrats," the NRCC crowed in a memo last week in response to the Carville-Greenberg warnings.

An NRCC internal poll of likely voters in 50 targeted districts held by Democrats is fueling GOP hopes they will benefit from the Democrats' troubles. It showed, among other things, that "voters are not only frustrated with the new majority's inability to get things done but that voters are not at all loyal to their current Democrat member and are in a firing mood."

Notably, the poll found that "only 35 percent of the voters say they will vote to re-elect their current Democratic congressman in these districts. Half -- 50 percent -- prefer someone new."

Another bullish sign for the GOP, House candidate recruitment "is way up," officials told me.

Carville and Greenberg disagreed, pointing to their own polling of 1,451 likely voters July 25-30 in 35 key congressional districts that show their incumbents holding "dramatic leads" over any Republican challenger. But none of the polls may mean much until one can match real live candidates against one another in the general election.

Clearly, congressional Democrats and their leaders have failed to meet the minimum expectations of the voters who elected them, as the latest poll numbers attest. This opens a window of opportunity for Republicans and the White House to sharpen issues that will help strengthen their grassroots support and boost their share of independent swing voters who are up for grabs.

Still, Wasserman thinks a lot will depend on how the Iraq war plays out and whether it will dwindle as an issue if, as administration officials have been saying, preliminary troop withdrawals begin next year.

"We could see anything from a handful of small gains for Republicans in the House or a handful of Democratic gains," he said.