Nearly 1,000 angry coal miners and their families strained at the fence of the Sprouse Creek Processing Co. today, taunting company guards as tensions escalated in a 4 1/2-month strike that mirrors the classic mine-field labor battles of another era.

When six trucks loaded with nonunion coal attempted to enter the plant this afternoon, 70 demonstrators sat in the highway until they were arrested by state police. On Wednesday, 56 demonstrators were arrested, and last night, a piece of mining machinery was firebombed at the Cumberland Village mine, which still is operating.

Leaders of the United Mine Workers of America and the A.T. Massey Coal Co., the nation's sixth largest coal producer, worry openly that the fragile calm at Sprouse Creek might erupt.

The standoff between company and union began late last fall over what seemed a technical point: whether the coal company and the union will have one contract to cover all seven company-owned mines in the area or separate contracts.

The company says the real issue is whether it can compete in an increasingly nonunion industry. The union says the issue is job security.

Whatever the reason it began, the strike gradually has been transformed from a relaxed picnic-like atmosphere where the company allowed pickets to use the parking lot and provided them with restrooms into a bitter struggle with civil disobedience and company-hired guards variously described as tough rednecks or scared kids.

The entire community has been drawn into the struggle.

Union leaders used bullhorns today to plead with the demonstrators to remain calm and force the company to make the next move in what Eddie Burke, a Washington-based official of the UMW, likened to a chess match.

As trucks rolled to a halt and police moved in, demonstrators complied with suggestions to cooperate when arrested.

On Wednesday, they forced police to carry them to a school bus, which had been commandeered to transport them.

But this is old-fashioned labor country, where using a school bus to take union members to court isn't tolerated. Today, the Mingo County School Board voted unanimously to reject a request from the state police to keep five buses on standby.

State police found an alternative, a bus owned by a church whose members include some of those arrested. Ellen Smith of Sidney, Ky., one of those arrested, said, "We sang 'Amazing Grace' and other church songs and had a ball."

School Superintendent Jim Melmige told State Police Capt. R.G. Fink that his was "an unreasonable request . . . placing the school system in the middle of labor and management."

At the Mingo County courthouse in Williamson, a large delegation sang union songs and lent moral support as their co-workers and friends were processed and fingerprinted on charges of obstructing an officer.

Among those arrested yesterday were three Hatfields and one McCoy, who long ago put aside their family feud and united in behalf of the union.

The 100 or so guards -- from security firms in Oklahoma and Ohio -- were described by one of their co-workers inside the fence as "a real bunch of rednecks who are looking for a fight," but a neutral observer said most of them look like "baby-faced kids barely out of high school who are scared to death."

Before the trucks interrupted the demonstrators this afternoon, they took advantage of the warm sunny day, which melted some of the snow on the hillsides to turn the shoulder of the road into a giant picnic ground where they munched pizza and sandwiches.

Despite pleas from their leaders to "give them a big smile for the cameras ; do not provoke them, that's what they want," an occasional rock was lobbed at the guards, prompting scattered cheers.

Sprouse Creek President James D. Slater was injured when attacked by strikers last month.

Today's crowd, which equaled the largest since mass turnouts were instituted by UMW President Richard Trumka on Monday, included several wives and a few children, including Lee Dean, 11, of Red Jacket, who skipped school "to picket with my daddy." They sang, chanted, called "good morning" to the uniformed guards -- who photographed the pickets' every move from behind the safety of a recently installed 10-foot-high fence -- and waved to a company helicopter that circled overhead.

A union leader said it may change tactics by reducing the size of the crowd, because "if we keep this many here, they'll want to go over that fence."