The United Mine Workers called a nationwide coal strike for 12:01 a.m. today amid new predictions that the country can do without the union's labors for most of the winter.

Raising the union's "no-contract, no-work" battle cry, UMW President Arnold Miller ruled out a contract extension yesterday despite reports of some progress in negotiating sessions here ever the last few days.

When the talks recessed last night, federal mediator Wayne L. Horvitz called it a pause so that both sides could reassess their positions. They will resume on Thursday afternoon, he said.

The strike is expected to idle about 160,000 UMW miners, mainly in Appalachia and the Midwest. But it would stop only half the nation's coal production - possibly less if work can be speeded up in non UMW mines. The UMW accounted for nearly 70 per cent of the nation's coal production when the current contract was ratified three years ago, but now produces only slightly more than 50 per cent.

Miller has said privately that a strike could last three months or more, although an immediate cutoff of health benefits and planned reduction in pensions - ordered because the near-bankruptcy of the union's benefit funds - raises doubts about the union's ability to withstand a long walkout.

In a statement issued shortly before the deadline. Miller accused the Bituminous Coal Operators Association, the industry's bargaining arm, of "trying to break this union" and said the strike will bring "hardships and human tragedy."

BCOA had no immediate response, but over the weekend the Edison Electric Institute released a report indicating that electric utilities have big enough coal stockpiles to carry most areas of the country through the winter.

Confirming earlier reports of extensive above ground coal supplies, the institute, an association of investor-owned electric companies, said utilities in regions heavily dependent on coal say they have reserves of about 100 days, according to United Press International.

"Although average utility industry stockpiles approximate 100 days, spot shortages could develop before winter's end," the report said. "However, intra- and inter-regional exchange of electric power should be sufficient to cover these instances."

The steel industry, the country's second biggest user of coal, also reports large stockpiles, enough to last through winter in most cases.

In his statement, Miller took a hard line about the union's bargaining demands: "I serve notice right now that the longer this strike lasts, the less likely it will be that we will reduce these demands." Ranks-and-file miners, he said, are "ready to take on this strike and stick it out until we win it."

Negotiating sessions are being conducted in a sixth-floor suite of the Capitol Hilton Hotel.

Although bargaining has been going on for two months, virtually no progress was reported until the Federal Mediating and Conciliation service took over the talks early last week and no major issues have yet been resolved, according to both sides.

The major roadblock is believed to be the operators' demand for greater stability in production, which has been curtailed by rampant wildcat strikes, coupled with the union's demand for a limited right to strike over local grievances. These have been mounting as labor relations in the coalfields sank to one of their periodic low points over the last few years.

Related to this is the union's demand for guaranteed financing of its medical and pension benefits, which the compaines say cannot be granted without some kinds of production guarantees.

The UMW-BCOA bargaining directly affects 130,000 miners and 130 companies. Another 30,000 miners working for companies that follow BCOA's example are also expected to strike. The union has a few thousand members in the West, where some independent contract settlements have been reported.