The most likely immediate impact of the coming redistricting, political analysts said, is that Republicans will be able to use their new power in the nation’s statehouses and governor’s mansions to draw new districts that will help the party strengthen its hold on the 63 seats in Congress that it picked up in November. When the new data comes in, both parties will use sophisticated computer software to begin carving up districts through politically creative cartography. But Republicans will have the upper hand, giving them the opportunity to add Republican voters to many districts where the party’s candidates won by narrow margins this year, making it easier for them to be re-elected.

“The Republicans are going to have their hand on the computer mouse, and when you have your hand on the computer mouse, you can change a district from a D to an R,” said Kimball W. Brace, president of Election Data Services, who has worked on redistricting for state legislatures and commissions.

Redistricting, it is often said, turns the idea of democracy on its head by allowing leaders to choose their voters, instead of the other way around. The new lines are drawn once a decade, after every census, to make sure that all Congressional districts have roughly the same number of people, to preserve the one-person, one-vote standard. But as a practical matter, both Democrats and Republicans often use it as an excuse to gerrymander districts for their own political advantage. This time, Republicans are better positioned to do it.

Tim Storey, an expert on redistricting at the National Conference of State Legislatures, said that Republicans were in their strongest position to draw lines in decades. Of the districts drawn by state legislatures, he said, Republicans have the power to unilaterally draw 196, four times as many as the Democrats. A decade ago, he said, Democrats had the advantage.

Texas will test the hopes of both parties. Democrats said that since much of the population growth was among minorities that traditionally support Democrats, they should benefit when Texas’s four new Congressional districts are drawn. Republicans, who control the process, said that much of the growth took place in Republican areas, so they will be able to draw more Republican seats. Tension lingers from the state’s redistricting in 2003, when Representative Tom DeLay, then the House majority leader, helped Republicans gain a large advantage in Texas’ House delegation.

Martin Frost, a former Democratic congressman whose district in the Fort Worth area was split during that redistricting, said he thought the Democrats would have a good chance of getting two of the four new seats, especially given the federal Voting Rights Act, which is supposed to ensure that the new lines do not dilute the voting power of minorities. And he said that the first order of business for Republicans would likely be to consolidate the gains they have made in recent elections by strengthening the districts of the party’s incumbents.