A spokesman for the nation's coal operators warned the United Mine Workers union yesterday that it faces the "beginning of the end" of nation-wide coal bargaining unless it can guarantee an end to wildcat strikes.

The warning from Joseph P. Brennan, President of the Bituminous Coal Operators Association, came as the UMW Health and Welfare Funds suffered another aftershock from its most recent wave of unauthorized work stoppages.

The funds, which earlier ordered a cutback in health benefits, had to take a short-term loan because income from production royalties was insufficient to cover $20 million in pension payments due this month.

Brennan, in a speech to the West Virginia Chamber of Commerce, said the wildcat strikes - which idled up to half the union's 175,000 working members before they started to wind down last week - have "eroded the integrity of the contract which is the corner-stone of labor management relations" in the coal industry.

Speaking of this fall's negotiations for a new three-year contract between the UMW and the BCOA, the industry's bargaining arm, Brennan said:

"1977 is a year that will mark either a new beginning of the historic cooperation between labor and management in coal or it can well mark the beginning of the end of a national coal labor agreement."

Brennan's threat raised the possibility of company-by-company bargaining or a return to the regional bargaining that characterized the industry before it moved toward national contracts in the late 1940s.

The UMW's share of coal production has declined to roughly 50 per cent in recent years and loss of the national contract could sharpen the decline, according to labor and industry sources.

The situation poses a "threat to the very existence" of the union, said Brennan, onetime UMW officials.

Brennan said this year's negotiations must include "some type of contractual mechanism to control and ultimately eliminate the wildcat strike without resorting to gimmicks and institutionalizing work stoppages" - a thumbs-down on many miners' and union leaders' demands for a contract-sanctioned right to strike over local grievances.

Brennan did not specify what the "contractual mechanism" might be but hinted at denial of health and welfare benefits to those who engage in wildcat strikes.

Since the current contract was approved in 1974, wildcat strikes have cost $340 million in lost wages and $108 million in royalties to the health and pension funds, Brennan said.

At a press conference after the speech, Brennan said nonunion forces out to "further their own ideology" may be behind the strikes. He did not elaborate.UMW President Arnold Miller has made similar allegations.

The strike continued to wind down yesterday, with about 20,000 miners still out, according to industry tallies. Both union and industry sources said they expected the back-to-work trend to continue.