WASHINGTON — Sen. Barack Obama has all but settled on his choice for a vice presidential running mate and set an elaborate rollout plan for his decision, beginning with an early morning alert to supporters, perhaps as soon as Wednesday, followed by a trip to swing states by the new Democratic ticket, aides said.

Obama's deliberations remain remarkably closely held. Aides said a half-dozen advisers were involved in the final discussions in an effort to enforce a command that Obama issued to staff: that his decision not leak out until supporters are notified.

Obama was said to be focused mainly on three candidates: Sen. Evan Bayh of Indiana, Gov. Tim Kaine of Virginia and Sen. Joseph R. Biden Jr. of Delaware.

Some Democrats said they still hoped that he would choose Sen. Hillary Rodham Clinton of New York or Gov. Kathleen Sebelius of Kansas.

By all indications, Obama remains likely to chose someone relatively safe and avoid taking a chance with a game-changing selection. A similar strategic choice now faces Obama's likely Republican opponent, Sen. John McCain, who has been under pressure from some Republicans to make a more daring choice.

Obama's advisers said he reached his decision while on vacation in Hawaii. They said it marked the end of what proved to be an unexpectedly intense process, condensed because he did not want to start actively vetting potential running mates before Clinton quite the race in June.

By contrast, McCain, who had wrapped up the Republican nomination months earlier, began his process in late spring.

That gave Obama's team of lawyers less time to review candidates, and several Democrats said it appeared that the list of candidates who were deeply vetted was limited to about a half-dozen people. (Campaigns typically check the background of candidates who are not necessarily in play, as a way of gaining favor with various constituencies or to keep the other party off balance.)

The team of advance workers and aides involved in planning the rollout — timed to galvanize Democratic voters as Obama heads to Denver next week for the party convention — have not been told who Obama will be selecting.

If all goes according to plan, the announcement will be made with text and e-mail messages to supporters early in the morning, in time to capture coverage on the morning news shows and take advantage of a full day's news cycle.

Obama and his new running mate will then begin a cross-country tour. Current plans call for them to be on the trail together for most of the time between the day of the announcement and the day Obama arrives in Denver, a week from Wednesday.

Obama's schedule calls for him to awaken on Tuesday in Orlando, Fla., and by the end of the day be in Raleigh, N.C. By Wednesday, he is scheduled to be in Virginia.

The Obama campaign has cautioned against reading anything into his schedule, saying it could be changed in an instant to accommodate the plan to introduce the running mate.

Aides said the announcement would come at the earliest on Wednesday morning, and no later than Friday.

Obama's advisers said they wanted to time the announcement to get maximum publicity going into the convention, after a stretch in which Obama was on vacation in Hawaii and McCain made good use of having the political stage largely to himself.

Democrats close to the process said the ability to turn up information through Web searches had made it easier for Obama's search team — Caroline Kennedy and Eric Holder, a former deputy attorney general — to plumb the backgrounds of prospective running mates with relatively little notice. In addition, because so many of the prospective running mates were senators, they were required to file annual financial disclosure reports.

Holder and Kennedy have been working largely out of Holder's law firm in Washington, using lawyers in his firm and others — many of whom are veterans of the process from having worked for Sen. John Kerry in 2004 and Al Gore in 2000 — to check the backgrounds of the potential candidates.

Obama was briefed frequently throughout the proceedings — receiving updates by telephone and e-mail — and came to Washington for a handful of meetings with a very small group of senior advisers in the law offices of Covington and Burling, where Holder is a partner. With the vetting concluded, there was no activity on Monday in the firm's suite of offices on Pennsylvania Avenue.

In contrast to previous selection processes, Obama has been largely spared the obligation of staging elaborate cloak-and-dagger processes to interview prospective running mates because he has been campaigning with them in close quarters, giving him a chance to get to know them.

The rampant speculation during the selection process encompassed many of the best-known names in the party, from Kerry and Gore, to Sen. Christopher J. Dodd of Connecticut, Sen. Jack Reed of Rhode Island, Gov. Bill Richardson of New Mexico and former Sen. Sam Nunn of Georgia.

The big choice for Obama, advisers said, was the extent to which he needed to choose someone who would fill perceived holes in his resume — lack of experience, particularly in foreign policy — versus a candidate who would reinforce his promise of change or one that might help him win a contested state.

Biden, the chairman of the Senate Foreign Relations Committee, falls into the category of helping Obama on foreign policy, while Kaine is a relative newcomer to national politics and would reinforce the notion of change. Both Kaine and Bayh would help Obama in a state that Democrats are trying to put in play.

For all the attention to Obama's deliberations, it is by no means assured that his choice will make a big difference in the outcome of the campaign.

"It's not that important," said Matt Bennett, the co-director of Third Way, a moderate Democratic advocacy group that has not taken a position in the race.

"Vice presidential candidates can make a marginal difference," Bennett said, "but they rarely matter in terms of winning a state or region — as Mike Dukakis and John Kerry found out. And a weak candidate doesn't really drag the ticket into the drink — as George H.W. Bush found out."

Still, the choice will provide Obama a chance to reclaim the public spotlight after what many Democrats say has been an unsteady patch, setting the tone as he heads into his convention in Denver next week.

The staff members of the vice presidential team reported to duty in Chicago two weeks ago, not knowing who they would ultimately be working for.