Senate Minority Leader Robert C. Byrd (D-W.Va.) yesterday negotiators for the United Mine Workers union and the Bituminous Coal Operators Association to return to the bargaining table "as soon as possible" to end a national coal strike, now in its second week.

"We can't really endure it very long," Byrd said of the strike that began, March 27 after the expiration of a three-year contract between the union and the BCOA.

He said a lengthy coal strike would seriously affect the economy of the nation, as well as that of his home state West Virginia.

"Coal has a very important contribution to make to the national economy and to the national energy picture," Byrd said yesterday on "Face the Nation" (CBS, WDVM). "I would hope that the leaders on both sides would get together as soon as possible and renew their negotiations."

A new round of talks was made necessary last week when UMW members employed in soft-coal fields in the East and Midwest overwhelmingly rejected a tenative, three-year agreement their leaders worked out with BOCA officials. The action angered both union and industry leaders, and some of the industry leaders said they would not return to the bargaining table until the miners "cool off" and get out of their "rejection mood."

Yesterday, the two sides still seemed far apart. UMW spokesman Eldon Callen said in an interview that his organization supports Byrd's call for a resumption of talks "as soon as possible." But, Callen said, "Right now, it doesn't seem that anything has changed."

B.R. (Bobby) Brown, chairman of and chief negotiator for the BOCA, was similarly pessimistic in an interview with United Press International. "I'm not optimistic. There is nothing planned," Brown was quoted as saying.

Industry sources have said repeatedly that they have enough coal stockpiled -- about four months' worth -- to withstand a long strike. But some concern was developing over the weekend about possible strike damage to the domestic coal industry's export business.

Last year, the domestic industry shipped 72.8 million tons of coal overseas and 17.1 million to Canada, for a total coal export tonnage of 89.9 million, a jump from the 64.7 million tons exported in 1979.

The United States competes with Australia, South Africa, Canada, the Soviet Union and Poland in the coal export business, but the United States, according to domestic industry sources, is often "the supplier of last resort" because of its antiquated coal transportation network and its labor problems.

"We had hoped to get a quick contract settlement this time to demonstrate to foreign buyers that we're a stable, growing industry," one industry source said in a weekend interview. "This strike may have thrown a wrench into all of that."

Most of the United States' overseas coal shipments originate from the East and Gulf coasts. Industry sources say it normally takes two to three weeks before a national coal strike affects those shipments.