In what would for them be an unprecedented step, environmental groups and other left-leaning organizations are mulling early endorsements in the Democratic presidential contest in hopes of heading off an extended nomination fight that might sap the party of resources needed for the battle to oust President Bush.

At the head of the line are key Democratic stalwarts such as the Sierra Club and Planned Parenthood that have traditionally shunned such a step — even in the general election — for both diplomatic and practical reasons.

The groups suggest they would use their endorsement to help build consensus behind one candidate in the pack, which includes six current Members of Congress. In their nightmare scenario, no candidate emerges from the Democratic primaries with a clear majority of delegates, and the remaining contenders battle through to the party’s late-summer convention while Bush firms up his position for the fall.

The nightmare ends with Bush’s re-election.

“We’ve never had something like this,” said Carl Pope, the executive director of the Sierra Club, referring to Bush. “This isn’t the second coming of Reagan. This is something much, much darker.”

Pope indicated, nonetheless, that his group would hesitate to make an endorsement before a “clear candidate” emerges. That means it is doubtful any step will be taken before the Iowa caucuses and the New Hampshire primary have been run.

“If there’s a candidate with good environmental credentials who looks to be emerging from the field, we’ll look very closely at making the endorsement,” Pope said.

Betsy Loyless, the political director of the League of Conservation Voters, agreed.

“These are different times,” she said, echoing Pope’s assessment of the Bush presidency. Loyless cautioned that her group is still only “considering” whether to endorse in the primaries. But, she added, “The LCV is looking to see if it is possible to single out one Democratic candidate on the basis of the criteria we use to judge a candidate’s environmental record, and on the viability and vibrance of their candidacies.”

Many of the liberal groups that provide the Democratic Party’s political infrastructure have traditionally been loathe to pick from among friends in primaries. Even general election endorsements are sometimes viewed as too provocative because of the disparate political views of constituent members of the groups.

The Association of Trial Lawyers of America, for instance, works almost in lock step with the Democrats on policy matters, and can be counted on to provide great financial support to the party and its candidates around election time. But ATLA nevertheless shuns endorsements for president.

“We have members who support every candidate for president, including George W. Bush. So we just don’t do it,” said Carlton Carl, a spokesman for the lawyers’ group.

What has altered the plans of other liberal groups is a combination of factors, beginning with a feeling of almost bottomless enmity toward the policies of the Bush administration and fed by anxiety about the Democratic primary process, which has been front-loaded in the hope that the party will have a candidate to challenge Bush by early spring.

Complicating this scenario is the concern that no sure-footed frontrunner will emerge from the pack of nine current candidates. With a highly compressed primary season, even scarcely financed candidates may not face the kind of money pressures that typically force also-rans to leave the hustings.

As the thinking goes, marginal candidates might as well stick it out and try to leverage any delegate support for perks, such as a prime-time speaking slot at the convention. They might even take on a kingmaker role with the two or more contenders who still have a shot at the nomination.

Senior Democratic strategists are doubtful that such a scenario will play out. And they would appear to be even more skeptical that the liberal interest groups could produce a consensus candidate.

“The idea that they would be able to clear out the field is ridiculous,” a top adviser to one Democratic presidential campaign said. “The only thing that’s going to clear out the field is the voters. And they don’t go to the polls until Jan. 19 [in Iowa].”

The adviser suggested that the murmuring about endorsements among the liberal groups shows that they have a naive view of how the Democratic primaries will play out.

“There is zero chance that the Democratic nominee will not be known by the first Tuesday in March,” the adviser said.

Some liberal groups sense political opportunities for themselves in dangling a possible endorsement before the crowded Democratic field of candidates.

Planned Parenthood recently changed its internal rules to allow for endorsements of presidential candidates in the primaries and the general election, clearing the way for the group’s first-ever endorsement in a presidential contest.

Officials at the organization, which operates 900 clinics nationwide, hope the move will pressure Democrats to sharply articulate their positions on “choice” in order to win the nod from the organization. The group’s president, Gloria Feldt, said Planned Parenthood has installed political operations in Iowa and New Hampshire.

“I don’t know that we will endorse, but we will be there,” Feldt said in a recent interview.

One Planned Parenthood official said an endorsement scenario would likely be similar to the Sierra Club’s, with no action taken until after Iowa and New Hampshire. The main criterion will be electability.

“It’s more likely that we’ll let the process play itself out,” the official said, “but we still retain the option, if we choose, to endorse.”

By contrast, NARAL Pro-Choice America is hewing to the more traditional outlook, withholding its endorsement until the general election, when the Democratic nominee is almost certain to get the nod from NARAL.

“We don’t endorse in primaries,” said David Seldin, NARAL’s spokesman. “There are nine pro-choice candidates, all of whom would be far better than the current president.”

Among organizations on the political left, organized labor — fed by compulsory (as opposed to voluntary) membership dues — has traditionally stood as the glaring exception in terms of its approach to endorsements.

This cycle, former House Minority Leader Richard Gephardt (D-Mo.) has already collected endorsements from six labor unions. And many Democratic strategists credit the early nod from Gerald McEntee, the powerful president of the American Federation of State, County and Municipal Employees, with solidifying then-Arkansas Gov. Bill Clinton as the party’s choice in 1992.

This time around, McEntee and AFSCME have laid out a months-long pitch season for Democratic candidates seeking the union’s nod, and will poll the union membership sometime this fall. Along the way, candidates and their political shops are being called in for interviews with AFSCME’s executive council.

“Whoever we endorse will get an immediate political infrastructure of 1.4 million [AFSCME] members,” union spokeswoman Roberta Heine said.