The pursuit of big donors could be politically risky for Mr. Biden in a Democratic primary already infused with outrage about the influence of the wealthy in politics. Some of Mr. Biden’s rivals, including Senators Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts, have effectively sworn off high-dollar fund-raising altogether.

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In an email to Democratic donors in the Philadelphia area earlier this week, David Cohen, a former party operative who is now a Comcast executive, outlined plans for a major fund-raising event in the city shortly after Mr. Biden’s announcement, likely in the middle of next week, and encouraged potential attendees to mail their checks to Mr. Biden’s operation even before he joins the race.

Mr. Cohen’s email suggested that potential donors should raise $14,000 each, in increments of $2,800, the maximum contribution allowed, and listed a number of party leaders planning to support Mr. Biden, including former Gov. Ed Rendell of Pennsylvania and former Mayor Michael Nutter of Philadelphia. Plans for a Philadelphia fund-raising event were first reported by the radio station WHYY.

A spokesman for Mr. Biden declined to comment on the fund-raising activity or the timing of his entry into the race. Mr. Cohen did not respond to an email, but a spokeswoman for Comcast said he declined to comment.

Stephen A. Cozen, a Philadelphia-based lawyer and a longtime friend of Mr. Biden, confirmed he was helping to organize the Philadelphia-based event next week, laying the groundwork for what Mr. Biden’s backers hope will be a significant financial show of force.

“You can actually start raising money,” Mr. Cozen said, adding that they hoped but were not certain that Mr. Biden would attend the fund-raising gathering.

Both Mr. McInerney and Mr. Cohen assured donors in their emails that their checks would be returned if Mr. Biden did not ultimately join the presidential race.

Mr. Cozen, however, said he had no doubt of Mr. Biden’s plans.

“He’s going to run,” Mr. Cozen said.