The midterm elections are being closely watched to determine whether Republicans will have a majority in Congress for the next two years. But it is the outcome of a lower-profile battle over state legislatures that could strengthen the Republican Party for a decade.

Republicans are within reach of gaining control of eight or more chambers in state legislatures this fall, according to interviews with Republicans, Democrats and independent political analysts. That would give Republicans the power to draw more congressional districts in their favor, since the expected gains come just as many legislatures will play a major role in the once-a-decade process of redrawing district boundaries.

Republicans said that the expect to win control of house chambers in Indiana, Ohio, Pennsylvania and of the Wisconsin state senate, and they said that they saw at least a dozen other states where they have a reasonable chance of winning control of legislative chambers.

Democrats acknowledge that they will be fighting to preserve their slim majorities in at least 10 chambers — including state senates in New York, New Hampshire and Nevada — but say that they see opportunities to gain control of chambers in four other states.

Redistricting, it has often been said, turns the traditional definition of democracy on its head: Rather than allowing voters to choose their leaders, it allows leaders to choose their voters.

The new districts are supposed to reflect the population shifts measured by the census. In practice, though, officials in both parties often try to gerrymander districts to help themselves and their parties win more elections.

So both parties are working frantically to eke out victories in state legislatures, pouring resources into races that are traditionally measured by the number of doors knocked on, not the number of ads broadcast.

For Democrats, the prospect of legislative losses could not come at a worse time. Gains in the past decade have left them in control of both chambers of the legislature in 27 states, while Republicans control both chambers in only 14; eight states have divided legislatures. (One, Nebraska, has a unicameral legislature and nonpartisan elections.) Republicans are predicting that they will gain at least 10 chambers this fall, which they say would give them the power to redraw up to 25 congressional districts.

"That will have a huge impact down the line," said Ed Gillespie, a former chairman of the Republican Party who now runs a 527 organization called the Republican State Leadership Committee that expects to spend $18 million this year on state elections. "Not just on taxes, schools and roads and the important business of state government, but also in terms of representation for a decade in Congress."

Some independent analysts suggest that the Republican surge could be even greater.

Louis Jacobson, who analyzed state legislative races for Governing magazine, rated 21 chambers now held by Democrats as "in play," compared with only four held by Republicans. Larry J. Sabato, the director of the Center for Politics at the University of Virginia, predicted recently that Republicans could gain eight to 12 legislative chambers. Tim Storey, a senior fellow with the National Conference of State Legislatures, said that the way the midterm election was shaping up, "you could see Republicans easily have their best redistricting position in the modern era of redistricting."

Many of the factors making congressional Democrats nervous are at play in local elections as well: Frustration at the continuing economic downturn is being directed at incumbents and the party in power, Republicans have seen their popularity improving in some polls, and there are indications in recent polls that Republicans are more motivated to vote than Democrats.

But Democrats warn that it would be premature to write them off.

"As Mark Twain might say, the reports of Democratic state legislators’ deaths are greatly exaggerated," read a recent post by the Democratic Legislative Campaign Committee, a 527 group that expects to spend $20 million this year on legislative races.

Democrats noted that local legislative elections did not always follow the contours of national elections, citing 2004, when the Democrats won control of six more legislative chambers even as their party lost the race for president and seats in Congress.

Michael Sargeant, the campaign committee’s executive director, called the Democratic-held legislatures "the fire wall for the rest of the Democratic Party" in drawing the lines that will help decide who controls Congress for the next decade. Sargeant said Democrats had an opportunity to gain control of House chambers in Tennessee and Texas and Senate chambers in Kentucky and Michigan.

To an extent, the Democrats may be the victims of their own success: They have more to lose, because they have made steady gains for much of the past decade. There are 4,048 Democratic state lawmakers and 3,251 Republican ones, by Storey’s count.

But many Democrats are frustrated and alarmed by the prospect that they could see the gains they had made — with legislatures and governorships — eroded or erased just when it counts the most, before redistricting takes place.

Consider Pennsylvania. After population changes in the 2000 census cost the state two of its congressional seats, the state’s Republican governor and legislature set new, irregularly shaped districts favoring Republicans, setting off a legal battle that went to the U.S. Supreme Court, which upheld the new districts. Since then, Democrats have taken control of the state’s House and its governorship.

Now, on the eve of redistricting, when the state is likely to lose another congressional seat, the Democratic hold is looking tenuous. The governor, Edward G. Rendell, must leave office because of term limits, and the Republican nominee has been leading in polls in the race to succeed him.

As for the House, G. Terry Madonna, a political scientist at Franklin & Marshall College in Lancaster, Pa., gave the Republicans roughly a 60 percent chance of winning control.

"The Democrats are generally tarred with the brush of incumbency, and when the economy is bad and people are losing their homes, their 401(k)s, their investments, there is a tendency to lash out at those in power," Rendell said in an interview. "I think that’s advantaged Republicans."

The challenge for Democrats, the governor said, will be to capitalize on their enrollment advantage and get their voters to the polls.

In Indiana, another closely watched state, Gov. Mitch Daniels, a Republican who is sometimes mentioned as a possible presidential candidate in 2012, has made a priority of helping Republicans win control of the state’s House.

Daniels said in an interview that he had personally helped to recruit more than 20 candidates, and that he would spend at least several hundred thousand dollars from his political action committee, Aiming Higher, to help them win — largely, he said, because the Democratic-controlled House had resisted his effort to consolidate some state and local government entities, and to overhaul education in the state.

But he said that retaking the House would have an impact on redistricting as well.

"We expect and intend to have a very nonpartisan redistricting process," Daniels said, complaining that the congressional districts drawn 10 years ago had favored Democrats. "But the data tell us that any sort of fair redistricting is likely to improve Republican chances."

Storey, of the National Conference of State Legislatures, noted that since 1902, the party of the president had lost seats in state legislatures in every midterm election but two.

And with many polls indicating that Republicans are more motivated to vote than Democrats, the coming election could give Republicans a large redistricting advantage. A big wave, Storey said, would give them the power to unilaterally draw as many as 160 congressional districts, compared with just 40 for the Democrats.

And while Storey noted that district maps were just one factor in congressional elections — given the power of incumbency, fundraising and the quality of candidates, among other elements — "clearly, the makeup of the district is pretty key."

© 2010 The New York Times Company