Four Virginia coal miners assigned to maintenance duties in a remote, hillside mine near the Virginia-Kentucky border were missing and believed trapped yesterday more than a mile inside the mine after what seemed to have been a small explosion.

Rescue teams were reported late yesterday afternoon to have moved within 300 to 400 feet of the site where the men were last known to have been. Dust and smoke were said to be hampering their efforts to move faster along the 38-inch-high mine shaft. The shaft runs horizontally about 8,000 feet into a mountainside.

"It might be several hours (before they reach the site, but you never know what you might run up against," Sam Stafford, a spokesman for the federal Mine Enforcement and Safety Administration in Washington, said last night.

Fifty miners normally would have been working in the bituminous coal mine, but most were on vacation at the time, a mine spokeswoman said. The workers who were there mostly were assigned maintenance duties, chores that miners often call "dead work," one mine safety official said.

Some miners inside the mine at 10&05 a.m. yesterday told of hearing "a loud noise and vibrations," but others heard nothing, said Barbara Poe, wife of one of the mine's two owners. Mrs. Poe said she and others inside a small mine office about 200 yards from the mine's entrance "didn't hear it at all."

There was some initial confusion at the mine after the noise, which Mrs. Poe said could have been a rock slide, cave-in, or something other than an explosion. However, a dispatcher for the Lee County Sheriff's office said the accident was "an explosion for certain" and mine safety inspectors said the accident bore all the signs of a small explosions.

There was no fire and none of the other 14 workers were in the mine at the time were reported injured, Mrs. Poe said. Mine safety experts initially said there were 18 others in the mine, but were unable to confirm their figure last night.

Virginia State Police blocked roads leading to the mine, about five miles east of the Kentucky border, but by nightfall a large crowd of miners, safety officials, and relatives of the missing men had gathered at the mine, known officially as P & P No. 2 Mine.

Stafford, the mine safety administration spokesman, said the missing men were returning to one section of the mine to pick up some machinery at the time of the apparent explosion. He said rescuers have not heard any noise from the area where the men are believed to have been.

A rescue team from the nearby Westmoreland Coal Co., one of southwest Virginia's major coal producers, was on the scene within 40 minutes of the accident, but it moved "slowly and cautiously" because of fears about the mine's safety, Mrs. Poe said.

The mine is owned by the P & P Co. of St. Charles, Va., a small town in the southwest corner of Virginia about 420 miles southwest of Washington, P & P is jointly owned by Charlie Poe, 40, a lifelong resident of southwest coalfields, and his uncle, Clyde Poe, Mrs. Poe said yesterday.