After spending millions of dollars and untold energy to register voters this year, Republicans and Democrats are running neck and neck in registration drives in five battleground states, while Democrats have made notable gains in two others, a survey of recent figures suggests.

Neither party has gained a significant registration advantage in such hard-fought states as Florida, Colorado, Nevada, New Hampshire and New Mexico, a Washington Post study shows. The strongest gains for one party belong to Democrats in Pennsylvania and Iowa.

Still, advocates and analysts said unprecedented efforts by political campaigns and independent groups leave them better placed and better funded than ever to get new voters to the polls in what is expected to be a very close presidential election.

"It's a sign that these organizations are warming up for the main event, which is turnout," said Donald P. Green, a Yale University professor of political science. "In this race, which is so close, if a campaign registers a person and knows where to find that person, they will do whatever they can to get them to vote."

Each side is claiming success, but important details remain unknown in the frantic race to the finish. Registration figures are incomplete. Statistics are not kept by party affiliation in Ohio or in such critical states as Wisconsin and Minnesota, where the major parties and their proxies continue to wage a fierce fight and voters are permitted to register on Election Day.

Experts also caution that voter drives do not automatically translate into election results. Newly registered voters could stay home or be trumped by independents or waves of sporadic voters motivated to go to the polls.

A review of the most recent registration figures shows:

* In Iowa, Democrats have registered four voters for every new Republican voter since 2000. Since this year's caucuses, Democrats have outregistered Republicans by 9 to 1, narrowing the GOP lead in registration statewide to about 8,000.

* In New Mexico and Colorado, Republicans have outregistered Democrats by about one percentage point each. In freshly competitive Colorado, Democrats have beaten Republicans in this year's totals but remain behind when the past four years of registration are taken together.

* In Florida, Republicans have also registered slightly more voters. Rolls have grown by more than 1 million since the 2000 election in the state that President Bush won by 537 votes. But nearly half of the new registrations have come from less predictable independents and small-party loyalists.

* In Nevada, there is a 1 percent increase in the other direction, with Democrats overtaking Republicans for the statewide registration lead. As in other states, the group of registrants who gave no major-party affiliation grew far faster, adding 28,400 names.

* In New Hampshire, Democrats made up ground, but they continue to lag behind Republicans in statewide registration by 40,000 voters. In the eight months leading up to the 2000 vote, more voters registered than in the same period this year.

Media attention has made 2004 seem like a busier registration year than usual, but the numbers in New Hampshire suggest otherwise, said Secretary of State William M. Gardner. He added that the picture may change on Election Day, when he estimates 10 to 20 percent of voters will join the rolls.

Terry Nelson, national political director of the Bush-Cheney campaign, said Republicans are counting on a disciplined registration drive to yield votes for Bush. He said the GOP has registered 3.4 million voters nationwide since January 2003, paying particular attention to past voters who have moved within a state or from one state to another.

"The Republican National Committee has an exceptional voter file," Nelson said. "Overall, we feel pretty good. If you compare registration numbers, we've made good advances."

On the Democratic side, nonprofit organizations are registering voters. America Coming Together, the best-funded, has focused its $125 million budget on four battleground states where its workers report registering 366,000 voters.

Steve Rosenthal, the group's director, said: "In Florida, it has been pretty much toe to toe, we think, but in Ohio, Pennsylvania and Iowa, the folks on our side have totally cleaned their clock."

Pennsylvania will not complete its files until the last week of October, but a survey of major counties shows that Democratic efforts have paid off.

In Philadelphia, more than 35,000 Democrats have been added to the rolls since 2000, while Republicans have dropped by more than 22,000, election officials said. Democrats also gained in suburban Bucks, Delaware, Chester and Montgomery counties.

The news does not entirely swing the Democrats' way. In strongly Republican York County, the GOP has added 15,000 voters since 2000, double the growth among Democrats.

Joseph Passarella, director of voter services, said his staff has been working overtime and weekends for five weeks to handle the rush. "We installed 12 additional terminals. We have people from other departments working overtime and nights and weekends, too," he said.

Strategists in both parties believe the candidate who takes at least two of three among Pennsylvania, Florida and Ohio will win the White House. Yet assessing the Ohio registration drive is difficult because the state does not include party affiliation on its forms.

Interest is intense, however. State voting chief Chris Abbruzzese said more than 500,000 voters have joined the Ohio rolls since the March primary, pushing the statewide total above 7.7 million. The Bush-Cheney campaign said it has added 200,000 names, while ACT and a partner consortium called America Votes said they have registered 300,000.

In Wisconsin, where Democratic challenger John F. Kerry has a small lead in recent polls, voter registration is up by at least 200,000 this year, estimates Kevin J. Kennedy, the state election chief in Madison. He believes the rise is being driven by the high stakes and close race as much as by activist organizations.

"The municipal clerks are hearing from people who have been gone from the country for 20 years and they want to vote," Kennedy said. Sandra Wesolowski, city clerk in Franklin, near Milwaukee, estimated that 10 times as many people are calling to request registration forms and absentee ballots for their college-student children as in 2000.

Frank Newport, editor of the Gallup poll, said: "All of our internal indicators suggest a higher percent of the American general population is registered, and there is a higher level of interest, than in 2000."

Still, appraising registration drives is a dicey business, cautions Curtis Gans, director of the Committee for the Study of the American Electorate. "Don't do it," he has been telling reporters, "because you don't have any reliable numbers."

Gans, noting that "registration doesn't necessarily speak to turnout," said voter rolls grew nationally in 1996 and 1998, largely because of "motor-voter" laws, but turnout was down in both years. In 2000 and 2002, by contrast, registration was down but turnout was up.

"My instinct is we'll have higher turnout this year because of interest in the election," Gans said, "but it won't necessarily be connected to registration."

Experience shows that two-thirds of voters who take it upon themselves to register show up at the polls, said Green, the Yale professor. Less clear is the motivation level of the people who would not have registered if someone in a shopping mall had not approached them.

Green also said studies show that between 33 percent and 50 percent of people who register are doing so after a move, often from a different part of the state. All these factors make it tough to determine voter turnout.

"It could be 30 percent or it could be 70 percent," said Green, who studies voting patterns. "The Republicans have been quite good at registering their faithful, but the Democrats have had a larger effort overall. If both sides perform equally well, I think that means the advantage goes to the Democrats through sheer dint of numbers."

With polls in so many states within the margin of error, Newport said, "only a fool right now would begin to say this state's going one way or another." Voter turnout efforts, designed to build on the registration projects, could prove pivotal.

"What we have even on election eve is the best estimate of everything we know," Newport said. "But it's possible on Election Day itself that driving people to the polls could change even what folks had thought they would do the night before."

Sleven reported from Chicago. Special correspondent Kari Lydersen in Chicago contributed to this report.