Federal mine safety inspectors said yesterday they had discovered an open cigarette lighter near the spot in a Southwest Virginia coal mine where four miners died Thursday in a methane gas explosion.

The inspectors refused to speculate if the lighter had triggered the explosion in a "worked out" section of the P&P Coal Co,'s No. 2 mine near the town of St. Charles. But they said the men were killed by an explosion of gas that obviously exceeded federal safety limits.

Rescue teams recovered the bodies of the four miners early yesterday after spending nearly 12 hours inching their way along more than a mile of the mine's principal horizontal shaft. Accumulations of methane, dust and blockage of the maine's ventilation system slowed their efforts, an inspector said.

In Washington, a spokesman for the U.S. Mine Enforcement and Saftety Administration said the agency would open a formal inquiry into the accident Tuesday and plans to question the 14 miners who were in the mine and escaped without injury.

John Pendergast, an official in the mine safety administration's Norton, Va., office, said yesterday that inspectors were unable to say whether the abandoned portion of the 8,000-foot-long shaft where the accident occurred had been inspected for methane gas before the men entered the area. Federal law requires that checks of methane levels be made every 20 miniutes in sections of mines where coal is being dug and requires all mines to be equipped with gauges to detect the ordorless, colorless gas.

Barbara Poe. wife of one of the mine's two owners and a spokeswoman for their mining company, said yesterday the mine always is checked for methane "two or three hours before the men come to work, or whatever time limit the regulations require."

One of the four miners killed in the accident, Harold Wells, 40, of St. Charles, was a crew foreman and assigned the responsibility for taking such readings, Pendergast said. Also killed in the accident were Harold Johnson, 33, also of St. Charles;Bill Perkins, 31, of Jonesville, Va., and Danny Tester, 29, of Woodway, Va.

Although federal inspectors described the mine, situated about five miles east of the Kentucky border, as a "moderately gaseous" mine, Pendergast said its daily accumulation of about 50,000 cubic feet of gas could easily be cleared by the mine's ventilation system. The system was blocked by the explosion and inspectors yesterday ordered the mine sealed pending their investigation.

Mrs. Poe said yesterday the mine had never been cited by mine inspectors for methane gas accumulations. Mine safety agency spokesmen in Washington said yesterday they were unable to confirm the mine's safety record because files on the mine were being brought to Washington for examination.