A coalition of national neo-conservative leaders gathered unobtrusively and unannounced here yesterday to hold a behind-the-scenes strategy "summit" and test their appeal to a new and seemingly unlikely constituency - traditionally democratic union labor.

The New Right leaders, many of them Washington-based fundraisers or lobbyists for conservative causes, approached their intended converts hesitantly, as if wary of being rebuffed in public.

But they were not as wary as the five union leaders who agreed to participate in the two-hour presentation of the argument that what's good for conservation is good for labor.

The unionist, saying they were worried about press attention and adverse reaction from the rank and file, insisted that the meeting be held behind closed doors and at a different motel than the one in which the New Right leaders were staying.

One of the union leaders who attended, United Steelworkers district director Frank Leseganich, denied later that he had been present.

Leseganich said he had heard of Rep. Philip Crane (R-III), who convened the meeting, and said, "From when I know about them [the conservatives], they can vote for bills in Congress to help labor, but I don't think they will." Leseganich, sounding nervous at a reporter's questioning, repeatedly denied meeting with the conservatives, even though sources positively placed him there.

By all accounts, the meeting, while not necessarily a love feast, was cordial and ended with promises from both sides to continue a dialogue on issue of common interest.

The union leaders showed up at the urging of former Youngstown Mayor Jack Hunter, a four-term Republican who established something of a rapport with labor while in office.

"Otherwise, I doubt if they would have come, " said one participant. Attending were representatives from steelworkers, building trades and carpenters locals.

Crane, chairman of the American Conservative Union said he is confident that the New Right has the money, the expertise and the issues to put to use the discontent and restlessness of a potential union constituency that feels betrayed by both the Democratic and Republican parties.

And Crane maintained that the idea is not as pie-in-the sky as it sounds.

"What better place to start than in Youngstown, Ohio?" he asked in an interview. "This place is an economic disaster zone."

Even Youngstown Democratic Mayor J. Philip Richley, though convinced that conservatives are wasting their time in heavily Democratic northeast Ohio, had to admit that they picked a city ripe for proselytism.

"While this business seems more symbolic than anything, they might consider this fertile ground. The situation is pretty grim around here," said Richley.

More than 4,200 workers at the Youngstown Sheet and Tube Co., one of the nation's largest steelmakers, were laid off in September. An additional 5,000 workers are expected to lose jobs son at the Ohio works of U.S. Steel Co. in Brier Hill.

Unemployment in the Mahoning River Valley is hovering around 10 percent, and coal shortages stemming from the United Mine Workers strike are expected to force power cutbacks and more factory closings.

"This place is one of the first warning bells of the death of the American dream, unless somebody does something," Crane said. "What's plaguing Youngstown is plaguing Johnstown, Gary, Buffalo and many other cities. Why shouldn't we, as conservatives, appeal to people in these kinds of straits?"

The names in the group that traveled here read like a Who's Who of the New Right:

Crane, Rep, Mickey Edwards (R-Okla.); Richard Viguerie, conservative fundraiser and "godfather" of the New Right; Paul M. Weyrich, director of the Committee for the Survival of a Free Congress; Howard J. Phillips, head of the Conservative Caucus, and Texas Republican Committeeman Ernest Angelo and Massachusetts GOP Chairman Gordon Nelson, both supporters of Ronal Reagan.

A few leaders remain close to the Republican party, but most have become disenchanted with the party's moderate leadership.

The group's common appeal to the labor movement, Edwards suggested, is a natural conservative instinct of blue-collar workers who feel overtaxed or - if out of work - depriced of a chance to exercise their deeply ingrained work ethic.

"What they talked about was jobs - tariffs, trade agreements, protectionism and environmental laws that hurt industry. The fact that they are basically conservative doesn't surprise me," Edwards said.

According to participants at the metting, both sides diplomatically skirted such volatile issues as right-to-work and common-site picketing, where presumably there would be sharp differences.

Weyrich said a "turning point" in the meeting came when conservatives disassociated themselves from the Old-Guard Republican establishment, and concentrated on "gut issues." "It nearly blew my mind; I've never heard anyone in the movement talk as harshly about environmental law as these guys did," he said.

Both conceded that translating the rhetoric of such a meeting into political activitly would be difficult.

Youngstown has nearly a 3-to-1 Democratic registration, and the 19th Congressional District led Ohio in supporting Jimmy Carter in 1976, Richley said.

"This has got to be more than just a question of public relations strategy. It has to be a question of following up on key issues for a practical purpose," Phillips said.

"We have to break down their assumption that conservative equals Republicanism, and Republicanism equals big business."

One way to do that, he said is to run conservatives on the Democratic ticket. Another would be to "avoid treating unionists as one dimensional people, because we usually aren't on their side on many social issues." He suggested capitalizing on other issues such as gun control and abortion.

The conservatives agreed that one brief visit to Ohio will not build a new constituency. Crane said the ACU plans to sponsor similar sessions in other big labor cities this years.