In return, officials said, county Democrats are being asked to keep Mr. Franks's margin of victory smaller than 30,000 votes.

He was the county Democrat of the Year in 1991, and was a member of the Bucks County Executive Committee.

He was treasurer of the Harriman Committee, a gathering of county Democrats who discussissues outside the party organization, but left that post to run for office.

The engineering firm hired without bids to design the plan, for a fee of some $500,000, donated $2,000 to the county Democrats and $2,500 to the same "better government" panel.

To county Democrats, the departure offers a long-awaited opportunity.

"It's certainly a loss for Spano as far as controlling county Democrats," Mr. Cavanaugh said.

Such a board has long been favored by county Democrats, who took control of the County Legislature in January for the first time in 80 years.

Party leaders hope that Hillary Rodham Clinton's planned appearance today at a fund-raising event in Great Neck will bring in $100,000 for county Democrats.

The lesson would seem that if the county Democrats could overcome their internal problems and nominate appealing candidates, they could again win county offices.

Mr. Alpert said Mr. Ploski had never asked county Democrats for support.