Federal officials were warned by United Mine Workers safety experts in April that the huge Clinchfield Coal Co. mine here would "blow up" if buildups of combustible materials and potentially explosive coal dust at the site were not corrected.

But the U.S. Mine Safety and Health Administration did not increase its enforcement efforts at the mine prior to the June 21 methane explosion that killed seven miners and badly injured three others in the worst Virginia mining disaster in a quarter century, according to federal records and interviews with federal and UMW officials.

The accident has highlighted criticism that MSHA has been too lenient in enforcing the 1977 Federal Mine Safety and Health Act that was passed to prevent such disasters. Critics contend that the MSHA office in nearby Northon, Va., which has direct responsibility for inspecting the McClure mine, has been especially lax, issuing minor citations and light $20 fines for conditions that investigators believe may have contributed to the accident.

The Norton office has issued the lightest penalties for potentially serious safety hazards of any MSHA office in the country this year, federal records show.

"If they the MSHA officials had heeded what we said, and responded with effective action, then it the explosion could have been prevented," said Danny Davidson, the UMW's deputy safety administrator in Washington. "There's no doubt that that mine could have been operated safely."

Joseph A. Lamonica, MSHA's national administrator for coal mine safety whom Davidson says he informed of the union's concerns in late April, said federal enforcement efforts weren't increased because agency officials had no reason to believe safety problems at the mine were unusual.

"From my perspective, McClure was a mine that the district was dealing with," Lamonica said in an interview last week. "It was not something that I viewed personally as being one of the worst mines in the country or one that required special emphasis."

Officials of Clinchfield, Virginia's largest coal producer and a division of the Connecticut-based Pittston Co., refused to comment on the UMW's charges last week. Company President Gene Matthis had asserted in a press conference three days after the accident that the mine, known as McClure Number 1, was "one of the best coal mines in this country" and that the company "spared no expense" in safety.

At 10:15 p.m. on June 21, an underground gas explosion sent a curtain of fire sweeping through a section of the McClure mine, killing all seven miners, including a section foreman who was three days away from retirement and a 51-year-old woman miner who became the state's first female mining fatality. A team of 60 federal, state, and union investigators is now attempting to learn precisely what caused the blast.

But UMW officials say there was mounting anxiety about conditions at the site earlier this spring and that they made two separate efforts to alert MSHA officials. The UMW's Davidson said he was informed about conditions at McClure after local union safety officials conducted their own inspection here on April 12 and found what they said were 51 federal safety violations.

The union allegations were buildups of combustible materials, including trash, paper bags and wooden tubes, and potentially explosive coal dust in the section of the mine where the June explosion occurred.

Two local union officials say that on the afternoon of their inspection they complained to Clinchfield supervisors at the mine about the safety violations and warned of a possible "blow up" because of the mix of coal dust and methane gas.

Harold Hartsock, an UMW safety officer assigned to southwest Virginia, says he met the next day, April 13, in Norton with MSHA officials, including the Virginia district's chief of inspections.

"I told them if they didn't clean the mines up and keep it ventilated, they were going to blow it up," Hartsock said in an interview last week. "I was very concerned."

Hartsock said he also relayed his concerns to UMW official Davidson, who then called Lamonica, the MSHA's number three official.

"I told him Lamonica that they had serious problems down there that needed to be taken care of or something was going to happen," Davidson said. "I wanted him to shake up the district manager down there . . . . He said he'd look into it but I never heard back from him."

Lamonica said Davidson frequently calls him about safety conditions in mines around the country. He said he remembers talking with Davidson about McClure No. 1 in March after a coal wall at the mine collapsed and killed one miner, but that he does not have "total recall" of a conversation about the McClure mine during April or May.

"But if Danny has a recollection, then I'd say it took place," Lamonica said.

Critics of the MSHA say its reaction to complaints about enforcement at the McClure mines is symptomatic of an increasingly lax attitude towards safety hazards within the agency. As part of the Reagan administration's overall deregulation efforts, Assistant Secretary of Labor for Mine Safety Ford B. Ford has publicly chastised federal inspectors for writing "nitpicking" safety violations and called for a new attitude of "cooperation," rather than confrontation, with the coal industry.

Ever since, there has been a dramatic drop in the number and severity of safety notices and penalties handed out by the agency, according to MSHA records.

MSHA inspectors wrote 20 percent fewer violation notices last year than in 1980, and fines against coal operators dropped 54 per cent during the same period, from $19.5 million in 1980 to $9.1 million in 1982.

The issuance of "serious and substantial" (S & S) violations has slowed to a trickle, from 9,096 to 1,773, during the same two-year period, according to agency records.

UMW officials consider the level of S & S notices crucial because under the law such notices trigger tough enforcement action and stiff penalties, while non-S & S notices usually reslt in $20 fines against coal companies. At the McClure mine, 37 out of 40 safety violations found by MSHA inspectors since April were recorded as non-S & S, resulting in the $20 fines.

"They were citing serious violations as nitpicking violations," said Robert Phillips, a local UMW safety officer. "They the $20 fines were like a pat on the back of the hand."

Lamonica insisted in the interview that MSHA's new policies does not mean it has gone "soft on safety" and that, in fact, the number of mining fatalities and the fatality rate are at its lowest level in history.

"I realize that this is the popular theme," he said. "But there have been no instructions out of this office for our inspectors to go soft on safety . . . . In fact, half my time last year was spent out in the field talking to our inspectors trying to get them off that kick that MSHA was getting soft."

But some federal inspectors say it is not a message that has penetrated to the Norton office, MSHA's Virginia headquarters. Federal records that of all the violation notices issued this year by the Norton subdistrict, only 8 percent were recorded as serious and substantial--the lowest percentage of any MSHA office in the country and about one-third the national average.

"A lot of inspectors who go out and write an S & S citation against a company or an order to close a mine are then told to vacate them, to do away with them--or if they don't the officials will," said one official in the Norton office, who asked not to be identified.

"They'll lean on small coal operators, but they won't touch the big ones," he said. "It's gotten to the point where many inspectors have said, 'what's the use of writing citations if you're only going to get chewed out?' "

The MSHA district manager in Norton, Ray Ross, acknowledged that supervisors frequently overrule inspectors who write citation notices, but said that this is proper under the law.

"People make mistakes on things," Ross said. "At times, citations are thrown out because they aren't valid . . . . I think it happens frequently everywhere."

"Our people have never been told not to enforce the law," said Ross.

Since the McClure mine opened four years ago, this huge $77 million facility has been considered an unusually "hot mine," because it leaks 3 million cubic feet of methane gas every day.

One miner has died in the mine each year since it opened, making its fatality rate nine times the national average. During the past nine months, MSHA inspectors recorded 163 safety violations, including 40 for inadequate or faulty ventilation of methane.

Virtually all the citations for improper ventilation, buildups of coal dust and other hazards that investigators now believe may have contributed to the explosion were chalked up as nonserious and resulted in $20 fines.

At least one reason, union officials charge, is because of a close relationship between Clinchfield officials and the local MSHA office. John W. Crawford, Pittston's vice president for safety, was the former MSHA administrator for coal mine safety, and Monroe West, the Clinchfield safety director at McClure No. 1, served until 1979 as MSHA subdistrict manager in the Norton office.

West, in particular, "had a lot of influence with the MSHA inspectors," said Davidson. "He would follow the inspectors at the mine around and chew them out."

In a telephone interview last week, West refused to comment and referred all questions about the McClure mine to Crawford, who works in the Pittston office in nearby Lebanon, Va.

"I really don't have any comments at all on any of this," Crawford said.

The relationship between Clinchfield and its regulators also extends to the state level. Harry Childress, the director of the Division of Mines and Quarries and the chief state mining inspector, was, until his appointment last year by Gov. Charles S. Robb, a Clinchfield company official serving as assistant superintendent of McClure No. 1.

The day of the McClure disaster, Childress told a reporter that his agency had done its own inspection of the McClure mine in May and found nine safety violations, none of which was classified as an "imminent danger" and all of which were quickly corrected by the company. "I didn't feel we had any major problem at the mine ," said Childress.

UMW officials say the state enforcement is less stringent than MSHA's. Since state mining inspectors do not issue fines, their only weapon is to close a mine--a power that has not been used in the past several years, according to a state spokesman.