WASHINGTON — Senator Obama is planning a $50-a-ticket fund-raiser at Harlem’s Apollo Theater next week on his first campaign trip to the neighborhood, raising concern among some local supporters that the entry fee will be too pricey for many residents.

The Illinois senator’s bid to make a play for New York comes as Senator Clinton warned Iowa Democrats yesterday against nominating a presidential candidate who needs “on-the-job training.”

The Obama campaign is hoping to sell out the 1,500-seat landmark on November 29 and send a message that it will not cede the black vote on Mrs. Clinton’s home field. Hosting the event will be Mr. Obama’s top New York supporters, including Harlem’s state senator, Bill Perkins, and a handful of state and city lawmakers from Brooklyn and the Bronx.

While local Obama backers have been clamoring for a Harlem visit by the candidate, the campaign’s decision to charge $50 as an entrance fee in a low-income community has left some top supporters uneasy. Assemblyman Michael Benjamin of the Bronx, who is listed on the host committee, said it was his understanding that tickets would sell for $25. Told that the invitation put the price at $50, he said he would contact the campaign to request it be lowered.

A City Council member from Brooklyn who recently endorsed Mr. Obama, Charles Barron, urged the campaign to relax the entrance fee. “He should really rethink that,” he said. “He should let the masses in.” Noting Mr. Obama’s fund-raising success, Mr. Barron added: “I know he needs the money, but he does have $80 million.”

Mr. Barron is not listed as a host for the event and said he has kept his distance from the campaign so Mr. Obama would not be forced to answer for his more radical policy views.

Mr. Perkins indicated that discussions were ongoing about how to accommodate people who could not afford the $50 ticket, but he said he could not be more specific. “We’ll be able to work that out,” he said.

The campaign declined comment on those plans.

A Brooklyn assemblyman, Hakeem Jeffries, said he had no problem with the dollar amount but encouraged the Obama campaign to supplement the fund-raiser “with free events in the near future to address the accessibility concerns.”

A campaign spokeswoman, Jennifer Psaki, said that while no open events were scheduled for next week’s visit, Mr. Obama would return to the city. “This is one of many trips that the senator will be making to Harlem, the Bronx, Brooklyn, and Queens,” she said, “and he hopes this will be the beginning of a long relationship with the community.”

The lawmakers all expressed excitement about the visit despite the price, with a Brooklyn assemblyman, Karim Camara, saying the arrival of the first “viable” African American candidate in the capital of black America would be historic. “This is going to be like Cassius Clay visiting Harlem in the 1960s,” he said.

Mr. Obama has previously held public events in Brooklyn and a major rally that attracted thousands to Washington Square Park in September.

The campaign announced the Harlem trip as Mrs. Clinton is sharpening her rhetoric on the question of experience. In a clear but unnamed swipe at Mr. Obama, the Democratic front-runner told voters in Iowa yesterday that electing an inexperienced president could result in the “costliest job training in history.”

“Every day spent learning the ropes is another day of rising costs, mounting deficits and growing anxiety for our families,” the former first lady said in an economic speech. “And they cannot afford to keep waiting.”

Mr. Obama, campaigning elsewhere in the state, replied by questioning Mrs. Clinton expertise in economic policy. “My understanding is she wasn’t Treasury secretary in the Clinton administration. I don’t know exactly what experience she’s claiming,” he said, according to the Associated Press. “Rather than just assert experience, if she has specific differences with me in regard to economic policy then let’s have that debate.”

Mrs. Clinton has mostly focused her attacks throughout the campaign on the Bush administration and on Republicans, but her comments yesterday, which follow her jabs at a debate in Las Vegas last week, signaled a new strategy of engaging her Democratic rivals more directly.

An Obama spokesman, Bill Burton, said later that Mrs. Clinton was “panicked” by the polls, which show a tight race in Iowa. An ABC News/Washington Post survey of likely Iowa caucus-goers released yesterday had Mr. Obama ahead by 4 points, although other polls have shown Mrs. Clinton maintaining a small edge.

The candidates stumped in Iowa yesterday after a skirmish over the weekend in which columnist Robert Novak reported that the Clinton campaign was withholding “scandalous” information about Mr. Obama. The Clinton campaign denied the report. Mr. Novak appeared on Fox News yesterday morning to defend his column, although he said it did not come from a source directly involved with the Clinton campaign.