The three helicopters touched down one at a time at the private heliport yesterday, depositing their passengers -- including Interior Secretary James G. Watt, Gov. John N. Dalton and the man who hopes to succeed him, J. Marshall Coleman -- for a fund-raiser in this town of 2,500 in Virginia's booming coal country.

Over cocktails and seafood hors d'oeuvres, about 90 coal company officials and their wives listened to Watt, the Reagan administration's controversial point man in its effort to relax strip mining and mine safety regulations, extol "the new federalism" and promise a close "working relationship" with Coleman. The guests then pledged more than $100,000 to the Republican gubernatorial candidate, according to campaign aides.

It was Coleman's latest raid on the coffers of Virginia's coal barons, and once again was orchestrated by Dalton, his closest political ally, and featured a Reagan cabinet officer. A similar gathering at the Governor's Mansion in February, with Energy Secretary James B. Edwards as the guest attraction, reportedly netted Coleman nearly $300,000.

Coleman's Democratic opponent, Lt. Gov. Charles S. Robb of McLean, has also been working the coal fields, preaching the same conservative gospel of less government regulation, more strip mining and solemn allegiance to the state's Right to Work law. Robb's campaign claims he raised about $250,000 in a sojourn here last winter.

Neither candidate's contributions must be disclosed publicly until October, a month before the state's elections. But already it is clear that both have far exceeded the amounts raised four years ago when coal interests first surfaced as major Virginia campaign contributors, giving Dalton $109,000 and his Democratic opponent Henry E. Howell $103,000. It is also clear that again this year the miners are following their practice of giving to both sides.

"Robb's less blatant about it, but he's not turning their oney away," said Frank Kilgore of Citizens for Better Reclamation, a surface-mining organization based in nearby St. Paul. "Whoever wins, the coal industry wins."

Reporters were banned from last night's party, but Coleman press aide David Blee said afterward that Watt, Dalton and Coleman made appeals similar to the speeches they gave earlier last night at a public rally in a half-filled auditorium in nearby Richlands.

"We didn't promise anything specific other than they'll have our ear just like other Virginians," said Blee. "They weren't sitting around tables tossing around $100,000 bills."

Still, the message was one the mine owners clearly liked. Watt had told the rally, "We've got to create jobs and improve our quality of life." In an interview, Watt boasted of plans to cut back Interior's Office of Surface Mining by reducing its local offices from 42 to 22 and its employes from 1,000 to 600. The responsibility for regulating strip mining and mine safety, he said, would be largely turned back to the states, an action Dalton and many miners here have long championed.

And Coleman, who led an unsuccessful legal challenge to the 1977 federal strip mining law, made clear how Virginia would respond if he were elected. "We've just about handcuffed our coal miners, and I mean to change that," he told a press conference. "The miners tell me that when federal inspectors come in they're very arrogant and dictatorial, and that's just counterproductive."

Watt arrived with Dalton at the Richlands airstrip sporting a blue "I Want to Live" lapel button, which he said referred to President Reagan's televised explanation of his tax-cut program. But the button could just as easily have referred to Watt himself, who has been under constant fire from environmentalists because of his hard-line pro-development views.

Coleman said he thought Watt's support would help his campaign -- "He certainly hasn't hurt President Reagan's popularity," Coleman said -- but others disagreed. Some conservationist groups, which so far have stayed out of the governor's race, say they plan to reconsider because of Watt's appearance.

"Robb's views on strip mining are just as bad, but Coleman will get some backlash," predicted Edward Grandis of the Environmental Policy Institute in Washington, who said state conservationist groups plan to meet soon to organize a campaign contributions committee. "Tying oneself to Reagan is one thing, to Watt another."

But Dalton, who arranged Watt's appearance, called him "an asset. He's talking about a balanced approach to the future of America and in this state, his philosophy of government is popular."

Campaign aides had hoped for a turnout of at least 400 for the Richlands rally, but only about 200 persons showed up, many of them carrying signs denouncing Dalton for a recent state decision allowing a private company to merge the town's two hospitals.

"These folks don't give a hoot about James Watt," said Pat Cavanaugh, publisher of the Richlands News-Press, a local weekly. "They're mad about that hospital, and they'd be picketing if Jesus Christ himself were here."

Dalton and Watt ignored the signs. But Coleman, who'd spent the day campaigning in the area and ducking questions about the hopsital issue, disarmed the protesters by welcoming them to the rally. "I hope we always have a country where people are free to make their grievances known," he declared to applause.

The fund-raiser that followed, hosted by Knox Creek Coal Company owner Jack Lester and his wife Shirley, didn't appear on a printed campaign schedule handed out by press aide Blee. Local police, armed with guest lists and walkie-talkies, blockaded a road leading to the Lester home.

Coleman said the affair was "just a private party" and that Lester and his wife had requested no reporters. But his finance aide, Charles Tyson, was more blunt. "Even if she ((Mrs. Lester)) says, 'Yes, we're not going to allow the press there.