According to data released this week by the state Bureau of Elections, the number of Republicans on the rolls in Chester County is 147,257. All other registered voters total 158,886; of those, 111,916 are in the Democratic column.

In Delaware County, other parties outnumber the GOP, 193,858 to 189,386. The Democratic tally is 154,707 - cause for jubilation among party leaders.

"The impetus for this whole thing was the primary," said Cliff Wilson, chairman of the Delaware County Democratic Committee. "It is the historic nature of the candidates that has done this."

The changes in the two counties were not as dramatic as those in Montgomery and Bucks Counties, which have gone majority Democrat after decades as Republican bailiwicks.

Still, the shifts are significant. Since the November election, Chester County has added 19,599 Democratic registrants and lost 3,020 Republican voters. Delaware County has gained 21,924 Democrats and lost 7,620 Republicans.

Chester County Democratic Committee member Bill Scott recalled that "when I started in politics, the odds were 3-1" in favor of the Republicans. "This is good for everybody," said Scott, former president of the West Chester Borough Council. "We don't have a one-party system anymore."

Jay Johnston, chairman of the Norwood Republican Party in Delaware County, said he was not worried. Philadelphians moving into the lower part of the county tend to hang on to their Democratic registration, he said, but they would vote for the Republicans in local races, such as borough council.

"They see them do the job and do it well," he said. "Most people don't take their party seriously."

Joseph E. "Skip" Brion, chairman of the Chester County Republican Committee, predicted that the numbers would not hold past Pennsylvania's April 22 primary. He noted that Republicans had changed parties for the 2002 primary, in which Ed Rendell and Mike Fisher ran for governor.

"A lot of Republicans switched to vote in that primary, and then they switched back," Brion said, adding that good Republicans were looking to influence the Democratic contest one way or another. The latest voter-registration statistics "are numbers you cannot rely on as you move ahead in this race."

He compared the shift to Monday's NCAA championship basketball game, which Kansas tied in the final seconds before winning in overtime.

"I think it's Memphis with 30 seconds to go," said Brion. "The game isn't over yet."