HUDSON, Iowa — When Congress began its August recess, Democratic Sen. Evan Bayh of Indiana took a weekend off, then headed back to the Midwest — to Iowa.

"It's good to be out of Washington and back out in the real world," he told a small gathering of party loyalists at a Black Hawk County fund-raising dinner.

It may seem early for Bayh, who is eyeing a 2008 White House bid, to be campaigning more than 1,000 days before the next presidential election and not even 10 months since the last one. But he's not the first to arrive in Iowa, or to show up in New Hampshire, the two states that traditionally start the nominating process.

More than a dozen prospective candidates from both parties have visited the two states or taken other steps toward a possible run for president. For some, that has meant penning political books (Democratic Sen. Joseph Biden of Delaware); for others, toughening their stance on social issues to woo conservatives (Republican Govs. George Pataki of New York and Mitt Romney of Massachusetts), softening their credentials to woo moderates (Senate Majority Leader Bill Frist of Tennessee) or revving up their political-action committees (Republican Sen. John McCain of Arizona, Democratic Gov. Tom Vilsack of Iowa, Republican Gov. Mike Huckabee of Arkansas).

Many say they cannot remember an earlier or more intense start to a presidential campaign.

"As soon as I got into town last week people went through a laundry list of who's coming through," said Joe Grandmaison, a longtime Democratic activist who divides his time between Washington, D.C., and a home on New Hampshire's rugged coast. "My reaction was, 'My God! I plan to work on a tan.' "

But there is good reason for the early activity, observers agree. The 2008 presidential election is likely to be the first in more than 50 years without a president or vice president running — Dick Cheney has said repeatedly that he won't seek or accept the Republican nomination. Although opinion polls have established nominal front-runners on both sides — McCain and former New York Mayor Rudy Giuliani among Republicans, Sen. Hillary Rodham Clinton of New York for Democrats — analysts say the fight for the White House is unusually wide open.

"Right now you could flip a 12-sided coin and come up with the nominee," Craig Shirley, a veteran GOP strategist, said of the Republican race.

It will be more than a year before the presidential field is firmly fixed. Several of those who may run — including Clinton and Democratic Gov. Bill Richardson of New Mexico — must survive November 2006 elections before setting their sights higher. (Among others with terms expiring next year, Pataki has said he will not seek another term as New York governor, and Romney may follow suit in Massachusetts, the better to focus on a White House bid.)

That makes the next 16 or so months a time of tryouts and tire-kicking for would-be candidates, most of whom are actively reaching out to major donors, top party strategists and the most hard-core political activists. This small group of hyper-involved partisans provides the early money and support that eventually will allow the most successful contestants to build a nationwide following.

"Many of the candidates are known only as names and not individuals," said Bill Dal Col, a Republican strategist who ran publisher Steve Forbes' 1996 and 2000 presidential campaigns. "People in Iowa and New Hampshire want to get to know you individually, or feel they do. ... That kind of courtship takes a lot of time and effort."

It also is no small feat to raise the estimated $30 million to $50 million it may take to seriously compete for the presidential nomination in 2008. "Candidates have to look and see if, realistically, there is a way to get there," Dal Col said.

Not every candidate now mulling a White House run will follow through. Former Democratic Rep. Dick Gephardt of Missouri, for example, spent "an enormous amount of time" in 1998 and 1999 preparing to seek the presidency before skipping the 2000 race, said Steve Elmendorf, a top adviser at the time. He said the exploratory process was crucial to Gephardt's decision.

"A large part of it is getting a sense from the candidates' point of view of whether or not they really want to do this," Elmendorf said. "Lots of people want to be president, but they've got to figure out: 'What do I have to offer that's going to make people want me to be president?' It's not something people wake up with one morning crystallized in their head. A lot of it comes from being out there, talking to people, test-driving their message."

The speech Bayh delivered to the Black Hawk County crowd of about 60 partisans sounded familiar Democratic themes from the 2004 campaign: a call for energy independence, complaints about unfair trade and the federal deficit, and criticism of President Bush's handling of the Iraq war, although Bayh sidestepped his vote to authorize the use of force.

Bayh seemed to make a favorable impression on some of his Midwest neighbors just by showing up.

"I don't like watching someone simply on the tube saying this or that. I like to meet them in person," said Juanita Hockey, 71, a retired bookkeeper from nearby Waterloo, who said she never would support a candidate she hadn't personally inspected.

For his part, Bayh told reporters his visit was just "the beginning of a longer conversation" with Iowa voters. His three-day visit included a series of private meetings with activists across the state and several appearances in and around Des Moines, the state capital. Still, Bayh indicated he was not entirely sure he would run for president, saying a final decision would come no later than January 2007.

If the candidates, Democrat and Republican alike, are playing coy, most political activists are holding back as well, fearful of jumping on a bandwagon that could collapse before the contest is seriously under way.

"It's fairly cautious because you don't know who's going to get in to stay," said Steve Grubbs, a former Iowa Republican Party chairman who has spoken with two prospective GOP contestants so far but plans to stay neutral for now. "If you get out there with someone who doesn't stick with it, suddenly you're sort of at the end of the line for someone you may sign up with ultimately."