Senator Obama stoked vice presidential speculation today with an unannounced stop at the Washington law firm of a search team member and then a flight to New York fundraisers with potential pick Senator Clinton and a second vetter.

“I’m not going to tell you” any details, the smiling likely Democratic nominee told reporters after spending more than two hours inside a downtown Washington office building where an attorney, Eric Holder, a member of his vice presidential search committee, has offices.

Mr. Obama wouldn’t say why he visited the building or whom he saw there, and the two top aides at his side — his campaign manager, David Plouffe, and his chief strategist, David Axelrod — also stayed mum.

The midmorning stop was one of at least two that weren’t on his public schedule, and aides would say only that Mr. Obama had private meetings planned while at Washington. They wouldn’t provide additional details, including whether Mr. Obama had met with Mr. Holder, a partner at Covington and Burling. The firm is located just blocks from the White House that Mr. Obama hopes to occupy come January.

Later, Mr. Obama was appearing with Mrs. Clinton, his rival-turned ally who is mentioned as a possible running mate, at two fundraisers spanning two days. A vice presidential searcher, Caroline Kennedy, accompanied the two on the flight from Washington.

Aides were tightlipped about why the trio traveled together other than to cite the fundraisers.

Ms. Kennedy introduced Mr. Obama at one fundraiser this evening, asking donors to “pledge to do all we can to elect Barack Obama.” She did not mention the running mate search. Mr. Obama, for his part, praised Mrs. Clinton, who was not present. He had finished speaking but returned to the microphone to ask his donors to help Mrs. Clinton retire her debt by filling out fundraising forms left on every chair.

At a second, smaller event for larger donors, Mrs. Clinton introduced Mr. Obama as “the person who should take the oath of office next January when we finally see the end of the Bush administration.”

They also were appearing together at a third fundraiser tomorrow morning.

Just before leaving Washington, Mr. Obama and Mrs. Clinton greeted each other on Mr. Obama’s plane and chatted in the aisle for several minutes before takeoff, but they otherwise didn’t speak. Mrs. Clinton sat in the first row on the right side of the plane; Mr. Obama sat in the second row on the left and slept for much of the flight. Ms. Kennedy sat at the front of the plane near the two senators.

Earlier today, Mrs. Clinton deflected a reporter’s inquiry about whether she has turned over her personal financial documents for Mr. Obama’s campaign to review as part of the vice presidential search, or whether she’s even been asked for such records.

Mr. Obama also spent part of the afternoon at a hotel near the Capitol. His campaign didn’t announce that stop either and also refused to disclose details of it.

In a city that revels in the intrigue surrounding a vice presidential pick, Mr. Obama’s unannounced stops and traveling companions fueled the guessing game about who he would choose for the No. 2 spot on the Democratic ticket — and whether he met with any of them at Holder’s office or, perhaps, elsewhere at another time.

Several people thought to be on Mr. Obama’s list have indicated they lack interest in the job. The latest was Senator Webb, who this week said he had told Mr. Obama he intended to remain in the Senate and “under no circumstances will I be a candidate for vice president.”

Both Mr. Obama and Senator McCain are trying to keep a tight lid on their searches, including only a small handful of top aides in the discussions to make sure the vetting process is as discrete as possible.

Nonetheless, each candidate is believed to be deep into the process of picking a vice presidential candidate. They may even be to the point of asking potentials for records, such as tax returns, financial holdings, medical documents and military files, or secretly interviewing candidates face-to-face.

So-called “short lists” of prospects probably exist, given how long both campaigns have been weighing their options. Mr. Obama’s search committee, made up of Holder and Kennedy, has been working since early June, while Mr. McCain’s helper, attorney Arthur B. Culvahouse Jr., has been involved in the Republican’s efforts for a couple months.

Time is a consideration for both candidates as they narrow their choices, announce their selections — and hope it produces a bump in the polls.

Typically, careful planning goes into the elaborate, staged “roll out” of a vice presidential pick to get maximum media coverage of what is perhaps the most eagerly anticipated decision a presidential hopeful makes before accepting their party’s nomination at the national convention.

Mr. Obama is making an overseas trip later this month to Europe and the Middle East, which could make a July announcement difficult. It’s also summertime and voters tend to pay little attention to politics, and Mr. McCain’s aides are mindful of that.

The window tightens more on Aug. 8 when the Beijing Olympics opens, running through Aug. 24. The Democratic National Convention at Denver runs Aug. 25-28, immediately followed by the Republican convention Sept. 1-4 at Minneapolis-St. Paul.

Today’s hint that Mr. Obama likely is fully engaged in the process began around 9:30 a.m., when his entourage, including a small contingent of reporters, left the Renaissance Mayflower Hotel, presumably to head to his Senate office so he could vote on a couple of bills later in the day.

A few minutes later and surprising even some of his staff, the motorcade pulled over and Mr. Obama entered the building housing Holder’s law offices through a back door labeled “Tenant Entrance Only.”

Mr. Obama spent most of the day on Capitol Hill for a series of votes, including on a bill overhauling rules on secret government eavesdropping.

By late afternoon, Mr. Obama’s campaign had disclosed that Mrs. Clinton and Ms. Kennedy would travel on his plane.

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Associated Press writers Nedra Pickler in Washington and Beth Fouhy in New York contributed to this report.