Pennsylvania, which voted Democratic in the 2004 presidential election by the narrowest of margins, has taken on a decidedly bluer look, based on the latest registration figures.

Since the April primary, Democrats have added to their record margin and now outnumber Republicans by almost 1.2 million statewide. And Democrats have made dramatic gains in Philadelphia's suburbs.

Analysts cite an extraordinary set of circumstances, including the hotly contested Pennsylvania primary - a race played out over six weeks - for pumping up the numbers.

They agree that while it is unclear how the registration numbers will affect vote totals, they will not work to the GOP's advantage.

"You would probably want to be a Democratic candidate, rather than a Republican," said Scott Keeter, director of survey research for the Pew Research Center, in Washington. A Pew poll also found Democratic gains in several other swing states.

Republicans have all but conceded New Jersey, where Democrats hold a 2-1 registration edge. But both John McCain and Barack Obama could qualify for frequent-visitor passes in Pennsylvania, where the campaigns had spent $27 million in TV advertising through the end of last month. Pennsylvania is one of the nation's richest electoral prizes, with 21 votes.

Pennsylvania's ratio of registered Democrats to Republicans, nearly 3-2, topped even that of 1976, after the GOP had been damaged by the Watergate scandal that drove President Richard M. Nixon from office.

Challenges could result in some changes to the final figures, which are expected next week. Through Monday, however, 8.7 million Pennsylvania voters had registered, an all-time high. Democrats have shown an unprecedented net gain of 614,008 in the last four years, which surprised even Obama's Pennsylvania organization, said spokesman Sean Smith.

"They are amazingly stunning," said Francis G. Lee, a political science professor at St. Joseph's University, who lives in Delaware County, where Democrats posted a net gain of 28 percent from 2004.

In 2004, only 150,000 votes separated Democratic nominee John Kerry and President Bush.

"There's no doubt they did a good job of registering voters," GOP spokesman Michael Barley said of the Democrats.

The Republican Party is "troubled" by the Democratic gains, but Barley questioned how many new voters would show up on Nov. 4, how they would vote, or how many of the registrations would end up being valid.

Republicans also have questioned the validity of thousands of new registrations, in Pennsylvania and across the country, collected by the Association of Community Organizations for Reform, known as ACORN.

A senior Philadelphia election official said yesterday that the city had discovered about 1,200 possibly fraudulent voter registrations - almost all of them submitted by ACORN - and had turned them over to the U.S. Attorney's Office for criminal investigation.

Patty Hartman, a spokeswoman for the U.S. Attorney's Office, said she couldn't confirm or deny any investigation. But she said, "We are aware that there are allegations out there against ACORN, and we are reviewing the allegations appropriately."

ACORN representative Ali Kronley said the organization had not been notified that the commissioners turned over suspect forms to the U.S. Attorney. But she said the number, 1,200, was consistent with ACORN's own records, which show that ACORN flagged 1,294 forms out of the approximately 85,000 it collected in the city.

In Philadelphia, the number of registrants, 1.1 million, actually exceeds the census count of the eligible population. The city has identified 58,000 "duplicate" registrations, and the actual number of eligible voters on the rolls is probably closer to a million, said the election board's Bob Lee.

Keeter, of the Pew Research Center, said that the final figures for Pennsylvania were unlikely to change much and would point to an extraordinary turnaround in a state where the GOP held mammoth registration advantages from the New Deal era through the 1950s.

In Philadelphia and the four suburban counties, Democrats gained 317,708, with a 22 percent jump in Chester County; 21 in Montgomery; 12 in Bucks; and 8 in Philadelphia, where Republicans are outnumbered 6-1.

In the once solidly Republican suburbs, the GOP advantage has fallen from almost 350,000 in 2000 to fewer than 20,000.

Similar shifts have occurred in other Northeastern metropolitan areas, such as New York and Boston, said Francis Lee. That is at least partly the result of people moving out of the city and taking their Democratic voting habits with them.

In Philadelphia's case, 2008 registrations got a mighty boost from the Pennsylvania primary race between Sens. Hillary Rodham Clinton and Obama, said Tom Lindenfield, a Washington consultant who helped organize the state's Obama registration drive.

The six-week wait between the Mississippi primary and Pennsylvania's, on April 22, allowed Democrats to focus efforts on signing up voters, he said.

Prospective voters were not only energized by Obama and Clinton. General dissatisfaction with the Bush administration and concerns about the Iraq war helped swell the voter rolls.

"You don't have that many big states that could have felt the same kind of forces," said Keeter.

Randall M. Miller, a history professor at St. Joseph's and a veteran political observer, said Democrats benefited from more than good fortune.

He said they were focused and well-organized and used the Internet and new technologies to recruit voters.

Said Miller, "They out-thought and out-hustled the Republicans."

It is too soon to determine whether Pennsylvania will lose its battleground status, the experts cautioned.

But should Obama win big in the state, it is possible that Pennsylvanians would see less of presidential candidates and their advertising dollars in future campaigns.

"Clearly," said professor Francis Lee, "they would be foolish to spend money in Pennsylvania."