United Mine Workers President Sam Church Jr. yesterday urged union members to prepare for a strike that he said could last as long as the record 111-day walkout that tied up the eastern soft-coal industry in 1977-1978.

Church's warning came as more than 12,000 miners taking part in wildcat strikes in six states seemed to be defying orders from local union leaders to return to work until the union's contract with the Bituminous Coal Operators Association expires on Friday.

"I find it necessary to publicly urge each and every UMWA member to stay on the job until the last minute of this contract at 12:01 a.m. March 27," Chruch said at a news conference here.

I am urging this because I now realize that it will be vital that they make every dollar they can make and save every dime they can . . . . What all this means is that this strike on March 27 could very possibly be even longer than the 111-day strike the last time around."

Church also said he was sending home the union's five-member negotiating team, which he said had been on standby here since Tuesday, when talks with the BCOA collapsed. The union's 39-member bargaining council, which would have to approve any tentative agreement before it is recomended to local leaders, was sent home Tuesday afternoon.

Tuesday's beakdown virtually assured a strike this Friday because the union usually allows its rank and file 10 days to ratify a contract. UMWA miners traditionally do not work without a ratified agreement.

Yesterday's action, coupled with Church's allegations that oil companies owning coal mines deliberately undermined the talks, indicated a growing, emotion-laden impasse in the negotiations, which began with both sides vowing to arrive at a peaceful settlement for the first time since 1964.

BCOA chief negotiator Bobby R. Brown said yesterday that the industry "wants to reach a tentative agreement . . . at the earliest possible time." However, he said, "resumption of negotiations can only occur when the UMWA indicates its willingness to modify its demands."

However, Church charged yesterday that industry negotiators are lying when they claim they want to bargain in good faith.

"We realize that no matter what the . . . negotiators from the BCOA might have told you or us, they had not intention of settling these negotiations without a strike," he said. "To them, the issues have never been the important factors. We would talk endlessly on one stalemated issue, and the next day they would bring up another item to keep the talks bogged down and unproductive."

Church said he has been calling the BCOA daily since the talks broke down Tuesday, but that his request for resumed bargaining was rejected because the union refuses to yield to an industry demand that if forgo royalties on "nonsignatory coal" -- coal produced in mines not covered by the union's national agreement -- that is purchased by BCOA producers.

The complicated arrangement stems from a 1946 agreement that requires "signatory" coal producers, such as electric utilites that own coal mines, to pay a royalty of about $1.96 a ton into the UMWA's health and retirement funds when they purchase "nonsignatory coal."

Firms such as electric utilities are required by law to buy low-sulfur coal, most of which is produced in nonunion mines in the West.

"This is an emotional issue for my people," said Church, who acknowledged that his union has no strike fund. But he said it will not give in on that point, or buckle under a srike, "no matter what happens."