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.