Democratic Party leaders greeted the news of Gary Hart's return to the presidential race with open skepticism and a resigned feeling that it further muddles a shapeless contest.

While none forecast that the Coloradan will emerge as the party nominee, some campaign operatives and consultants said they think that he can draw enough attention and support in early contests to prolong the primary battling and perhaps open the door for a brokered convention.

Senate Majority Leader Robert C. Byrd (D-W.Va.) reflected the general astonishment when he told reporters, "It's a crazy old world, isn't it?"

Georgia Democratic Chairman John Henry Anderson said that in his home town of Hawkinsville, "They think he's taken leave of his senses. He reminds me of Judge {Robert H.} Bork," Anderson said. "He wants to make the vote official."Bork, the unsuccessful Supreme Court nominee, insisted on a Senate vote long after his confirmation was doomed.

Hart got a distinctly cool reception from his party leaders and from the six active contenders for the nomination. "A big story for a day," said Democratic National Chairman Paul G. Kirk Jr., "but not much impact overall."

Sen. Paul Simon (D-Ill.), arriving in McAllen, Tex., for a candidates' debate, said, "I know Gary feels deeply about the issues, but I hope he isn't fooling himself. My concern is that we don't trivialize the campaign. We should not have a campaign that focuses on what someone did some weekend somewhere."

None of the other declared aspirants alluded as directly to the relationship with Miami model Donna Rice that drove Hart from the race seven months ago. But none went out of his way to make the erstwhile front-runner welcome. Massachusetts Gov. Michael S. Dukakis, who replaced Hart as the strong favorite in the Feb. 16 leadoff primary in New Hampshire, said the contest "is more than a symbolic exercise . . . and I intend to beat Gary Hart in New Hampshire."

Spokesmen for other campaigns disputed Hart's assertion that they were not addressing the issues and said they will not change their strategies because of his return to the race.

The first test for Hart, almost everyone said, is whether he can answer -- or avoid -- the personal questions about his character that led to his departure from the contest. "The key question is, will people give him a hearing, give him a chance," said pollster Patrick Caddell, who aided Hart in his 1984 race. Iowa Democratic Chairwoman Bonnie Campbell said, "The next 48 hours are critical . . . . If he isn't forthcoming and doesn't confront the {character} issue, he won't succeed."

Many questioned whether Hart, starting late and with many of his former supporters working in rival campaigns, can make himself a force in the battle for the nomination. "It's way, way too late," said Lorretta Bowen, political director of the Communications Workers of America. "He's broke; he has no organization. The name of the game this year is delegates."

While the Democrats pondered this latest twist in a bizarre pre-election year, gleeful Republicans said Hart's decision adds to the public impression that the Democrats are not serious about the 1988 contest. GOP national Chairman Frank J. Fahrenkopf Jr. said Hart's reentry "shows they are lost in the political wilderness and they don't have a leader." Fahrenkopf said that when he brought the news to an early morning White House meeting with congressional leaders, "No one believed it at first, and then they just laughed."

Some Democrats were equally chagrined. John McEvoy, a longtime Democratic activist who was a top adviser to Hart in 1984, said, "The only people who can be pleased are Jesse Jackson's supporters and the Republicans."

McEvoy's view, like many others, is that Hart is too scarred by the Donna Rice scandal to win the nomination but may be strong enough to throw the Democratic race further out of focus, perhaps prolonging the nomination struggle.

Caddell said, "This ought not to be laughed off. There is enormous disenchantment with the field, as reflected in the polls, and here's a guy who talks, not just about new ideas, but about big ideas."

Most polls have shown none of the Democratic candidates outdistancing "undecided," and there were some operatives yesterday who speculated that Hart could bounce to the top in the next round of surveys. But the message of past polls is equivocal.

A Gallup survey for the Nation magazine last July showed Hart leading with 25 percent of the vote, twice that of runner-up Jackson. Early November polling by Penn and Schoen for Spy magazine showed Hart and Jackson tied at 17 percent, with the other five active Democratic candidates well back.

But a September NBC News-Wall Street Journal poll showed that a 2-to-1 majority of likely Democrat voters opposed Hart's reentry into the race. A Washington Post-ABC News Poll in the same month found a 58 percent majority saying that Hart is qualified to be president and 28 percent saying he is not. His negative rating was second highest, behind Jackson's 31 percent.

The first readings from the battleground states indicated Hart was not shaking loose many supporters from other candidates. Reporters found Steve Lynch, Hart's Iowa van driver, who had signed on for a similar role with Dukakis, going back to his original favorite. But Teresa Vilmain, the former Hart coordinator in Iowa who has taken over the Dukakis campaign, said, "I'm with the Duke. And I'm staying with the Duke."

In New Hamphsire, Jackson campaign director Steve Cancian and Susan Calegari, cochairman of former Arizona governor Bruce Babbitt's campaign, said they would not return to the Hart campaign.

North Carolina Democratic Chairman Jim Van Hecke Jr. said most of Hart's "hard-core supporters were hurt by what happened last spring and went to other candidates. I don't see him being a strong candidate at all."

Florida House Speaker Jon Mills, who had headed the Hart campaign in that state and is now supporting Sen. Albert Gore Jr. (D-Tenn.), said, "I don't see how he {Hart} can do it without resources. Most of the people who were involved with Gary's campaign are with other people."

In another key "Super Tuesday" state, Texas Chairman Robert Slagle said Hart had been "ill-advised" to reenter the race. The public is "not ready to sanctify adultery as a national virtue," he said.

Despite the almost universal doubts about Hart repeating his 1984 role as Walter F. Mondale's toughest competitor for the nomination, some Democrats said they can see him becoming a key player in the 1988 struggle. Veteran Chicago politician William J. Daley, who is uncommitted, said, "I don't think it's out of the realm of possibility that he can be in the run all the way. Plenty of people have voted for Gary Hart already. And he's clearly going to make himself the lightning rod for everybody who thinks this field is a bunch of lightweights."

Pollster Peter D. Hart, who helped plan Mondale's 1984 strategy against Hart, said the Coloradan is offering people an opportunity "to do two things with one vote: vote against the field and vote against the media." Several other pollsters said strong resentment remains against the news media for its role in Hart's downfall. They suggested Hart may be able to capitalize on that feeling.

The first polling in New Hampshire following Hart's reentry shows him in second place behind Dukakis.

A telephone poll last night by Peter D. Hart Research for Philip Morris magazine reached 316 likely Democratic primary voters. It gave Dukakis 36 percent; Hart 23; Simon 10; Jackson 7; Babbitt 4; Gephardt and Gore 3 each; and undecided 14.

Before Hart's decision, a larger sample in the same survey on Nov. 19 gave Dukakis 50 percent and showed Simon second with 11.

Peter Hart said Hart's potential in New Hampshire appears to be limited. The Coloradan had a 34 percent positive rating but a 38 percent negative, while Dukakis had 61 percent positive and 18 percent negative.

McEvoy, while critical of Hart's motivation, said, "I think he could win enough delegates to screw it up for anyone else." He argued that the spotlight will be on Hart when the televised debates resume Jan. 15 and that in the "sanitized environment" of those forums, Hart is likely to be able to focus on broad national issues -- not questions of personal character.

McEvoy was one of several who suggested that Hart's decision ultimately could pressure New York Gov. Mario M. Cuomo (D) to reconsider his refusal to run. But Cuomo responded to the news with a statement reiterating his often-expressed belief that the nominee will come from the field of active candidates and saying, "I will help in every way I can to find and promote the best candidate possible in the present field . . . . "

Party chairman Kirk said Hart's decision does not shake his belief that one of the other contenders will gain enough momentum from the contests of winter and early spring to "start a bandwagon" that will secure the nomination.

Backers of several other candidates said Dukakis might suffer the most if Hart is able to revive his candidacy in New Hampshire, where he scored his breakthrough victory in 1984. But Leslie Dach, a Dukakis spokesman, said the Massachusetts governor would earn additional momentum by beating a field that includes Hart.

Fred Martin, manager of the Gore campaign, said, "To the extent that Hart takes away votes from the front-runners in Iowa and New Hampshire . . . it should help Gore."

Spokesmen for Rep. Richard A. Gephardt (Mo.) and Babbitt said Hart's reentry could benefit them. "Maybe what it does in the end is give a candidate like Dick Gephardt a chance to defeat a perceived heavyweight," said Mark Johnson, a Gephardt spokesman.Staff writers Maralee Schwartz, Bill Peterson, James R. Dickenson and Frank Swoboda and researcher Collette T. Rhoney contributed to this report.