As donors and activists fall into line behind the leading presidential candidates, polls show a substantial number of rank-and-file Democrats and Republicans yearning for candidates not currently in the presidential race.

Two of the most prominent noncandidates, Vice President Gore and a former House speaker, Newt Gingrich, routinely show up in the top tier in national surveys and sometimes land in second place in state-by-state polls. Others still reported to be toying with presidential bids, such as Mayor Bloomberg, Senator Hagel of Nebraska, and a former senator from Tennessee, Fred Thompson, are tracked by the press and debated by political pundits with a greater intensity than many of the declared candidates.

One presidential historian attributes this year’s bumper crop of presidential Hamlets to the lack of a sitting president or vice president in the field. “You do have a wide open possibility because there’s no incumbent and neither side has sort of fielded a candidate who instantly appears to be the answer to everything,” Robert Dallek of Boston University said.

Each of the major political parties has its own reasons for concern with the current field. The Democratic front-runner, Senator Clinton, is well-liked by members of her own party, but even some of her biggest fans harbor lingering doubts about her ability to win in a general election. Her nearest rival in the polls, Senator Obama of Illinois, lacks Washington experience and is untested in a national campaign.

Mr. Gore is the only potential candidate for 2008 who can boast of having won the popular vote in a presidential election.

In the Republican camp, prominent conservative leaders have expressed public misgivings about the top two contenders, Mayor Giuliani and Senator McCain of Arizona. A former Massachusetts governor, Mitt Romney, has tried to capture the conservative vote, but reports that he once held more liberal views on gay rights, abortion, and other issues have sapped enthusiasm for his bid.

The director of the Marist Poll, Lee Miringoff, said the phenomenon of the waiting-in-the-wings candidate is not uncommon, but the presence of figures as prominent as Messrs. Gore and Gingrich is rare. “To have two names that big is somewhat unusual because they really haven’t slammed the door shut. We’ve had people in the wings before, but they usually don’t come in after 20 people are running and half a dozen have already dropped out,” Mr. Miringoff said.

The highest-profile case of such indecision in recent years was Governor Cuomo’s flirtation with the Democratic nominating contest in 1992. Democrats impressed with the governor’s oratory beseeched him to jump into what was seen as a field of obscure contenders. Mr. Cuomo agonized over his choice until the last minute, prompting some reporters to travel to New Hampshire to cover him filing for the ballot.

“I was in the corridor in Albany that day. There was a plane on the tarmac pointed to New Hampshire,” Mr. Miringoff said. Mr. Cuomo never made the trip,

One longtime Washington observer, Stephen Hess of George Washington University, noted that some who don’t intend to run toy with the public in order to bring attention to themselves or particular issues. “Richard Nixon said virtually the same thing to me in ’64. ‘Let them think I’m a candidate for a while. It gives visibility to things I want to say,'” Mr. Hess said. “

Here’s a quick look at some of the most-discussed presidential prospects not currently in, or firmly out of, the race.

Contender: Vice President Gore
Chance of entry: less than 10%,
according to a former aide
Selling points: Hugely popular with the Democratic base; seen as soothsayer on global warming; could raise quick cash
Drawbacks: Could be tied to scandals of Clinton era; anti-Bush and anti-war rants might alienate swing voters

Contender: Fred Thompson, former Republican senator from Tennessee
Chance of entry: 50%, according
to a source close to Mr. Thompson quoted by National Review
Selling points: Widely known
from movies and “Law and Order,” could rekindle Reagan magic; acceptable
to moderates and GOP base
Drawbacks: Only eight years in the
Senate but nearly two decades as a lobbyist; support for campaign finance laws could irk some conservatives; presence in race of Wisconsin governor with the same last name could confuse headlines and debates

Contender: Mayor Bloomberg
Chance of entry: 80%, if Democrats and Republicans nominate candidates such as John Edwards or Mr. Romney,
according to a former mayoral adviser,
Ester Fuchs
Selling points: Can bankroll campaign from Bloomberg LP fortune; record as get-it-done manager in unwieldy
New York; running as an independent
could make him the ultimate outsider
Drawbacks: Shares some
“nanny-state” tendencies with Mrs. Clinton; New York sensibility might not play
in Peoria; untested in national politics

Contender: Newt Gingrich,
former House speaker
Chance of entry:30%
(Sun estimate)
Selling points: Conservative icon with a national following; future-focused; has built ties with some Democratic leaders
Drawbacks: Still detested by many
Democrats; lacked political savvy during government shutdown and impeachment crises; tends to make provocative
off-the-cuff remarks

Contender: Senator Hagel
of Nebraska
Chance of entry: 40%
(Sun estimate)
Selling points: Could consolidate Republican anti-war vote and pick up
Reagan Democrats; Vietnam background adds credibility
Drawbacks: Path to GOP nomination not apparent; advocacy for immigration
reform could neuter effort to win Buchananite constituency; talk of impeachment puts him to left of Democratic leaders