About 300 striking miners applauded United Mine Workers President Sam Church Jr., in Welch, W. Va., yesterday as he outlined the union's proposed contract with the coal industry and said he had made some serious mistakes in earlier negotiations.

The reception was in sharp contrast to jeers that greeted Church in many coal-field communities in March when he tried to sell an earlier contract proposal.

Voting on the tentative agreement to end the 67-day strike against the Bituminous Coal Operators Association is scheduled for Saturday. Church was in the second day of a six-state tour to brief 160,000 miners on the proposed contract.

"It sounds like a pretty good contract," said Welch miner James Floyd, adding that he wants to see the pact in writing before making a final decision. aCopies are to be distrubuted later this week.

Church said he had miscalculated union sentiment while negotiating the March proposal, which was rejected by more than 2 to 1.

Church said the new proposal in contrast, is a "good agreement."

Church reminded the miners that delegates to the UMW's latest national convention had voted to try to reach a new contract in 1981 without a strike. "I worked very hard to do that. But it seems I made a mistake in that there were two or three issues in the contract that were very emotional to you," he said.

Church plans to stop Tuesday in Kentucky, the nation's leading coal producer, and later this week in Virginia, Ohio and Pennsylvania.

Church said that despite the strike miners will get their regular two-week paid vacation this summer, but that the UMW also agreed to allow them to work voluntarily during their vacation period.