HARRISBURG - If there was ever a doubt about the public interest in the Democratic presidential primary in Pennsylvania, consider this:

On the last day to register, about 33,300 first-time voters signed up as Democrats and another 46,000 Pennsylvanians switched to the blue party.

By comparison in the same period, Republicans picked up about 6,000 new registrants and just 1,800 others switched to the Grand Old Party, according to the Pennsylvania Department of State.

Most of those new registrations and changes occurred March 24, the final day of in-person registration. Some were mailed in - before the deadline - and were received during the last week.

The contest between U.S. Sens. Barack Obama and Hillary Rodham Clinton has fueled the surge.

Not since 1976 have Pennsylvania voters had such a decisive say in who would be a presidential nominee.

"Pennsylvanians don't often get a chance to matter in presidential primaries, and this year they have the opportunity to play a key role in one of the best political dramas in a generation," said Chris Borick, a politics professor at Muhlenberg College. "They're seizing that opportunity."

Democrats in recent weeks topped the four-million-voter mark for the first time ever. Their totals now stand at 4.1 million, compared with about 3.2 million Republicans.

The numbers might even rise. County and state election officials are still processing voter applications that were postmarked as of March 24 - the deadline to register and to change party affiliation for the April 22 primary.

Contact staff writer Mario F. Cattabiani at 717-787-5990 or mcattabiani@phillynews.com.