Drive by the Walnut Street headquarters of Philadelphia's Democratic City Committee, and you can't miss the posters for U.S. Rep. Bob Brady's mayoral campaign.

Look at the committee's campaign finance report, and you'll find that in December it donated $20,000 to Brady's campaign fund.

That's no surprise maybe, since Brady is also the city Democratic chairman.

But the Democratic City Committee hasn't endorsed a mayoral candidate for the May 15 primary, and now two of the four other Democratic candidates say Brady ought to step down from his party post as long as he's running for mayor.

"The issue is your disregard for the obvious conflict of interest presented by your continuing to preside over the party and to control its apparatus while you are a candidate," State Rep. Dwight Evans and businessman Tom Knox wrote in identical letters delivered to Brady yesterday.

"It is precisely this contempt for a transparent and open process, where everyone is treated fairly, that contributed to the corruption and 'pay-to-play' culture of the current administration," the letter said.

Brady said in a phone interview last night that he wasn't moved by his rivals' letter. "I answer to 69 ward leaders, not two gentlemen," he said.

Asked if he thought it was fair that the city committee had made a $20,000 contribution to his campaign before having an endorsement meeting, Brady said, "I had no role in that."

Brady said restrictions in federal campaign finance law prohibit him from involvement in the finances of the city committee.

He referred questions about the $20,000 contribution to the party treasurer, State Rep. Frank Oliver.

Oliver didn't return a call to his office Monday.

Reached by phone last night, he hung up without listening to a reporter's question.

There's little doubt that Brady, who's been party chairman for 21 years, would be the overwhelming choice of ward leaders if an endorsement vote occurred.

In the past, the party has often avoided endorsements in contested mayoral primaries.

Two other mayoral candidates, U.S. Rep. Chaka Fattah and former City Councilman Michael Nutter declined to sign on to the Evans-Knox letter.

Nutter said he views Evans, Fattah and Brady as taking advantage of their positions as elected officials to run for office, so he sees the criticism of Brady taking advantage of his party post as "a distinction without a difference."

Nutter said he believes Brady should take a leave of absence from his chairmanship until the campaign is over.

A Fattah spokesman declined comment. *

Staff writers Catherine Lucey and Bob Warner contributed to this report.