The United Mine Workers and Bituminous Coal Operators Association reached tentative agreement early yesterday morning on a new three-year contract that union officials said would raise the combined pay and benefits of miners 36 percent over the next three years.

If recommended today by the union's 39-member bargaining council, and approved later by the rank-and-file, the agreement means the coal strike scheduled to start March 27 when the current contract expires will be no more than a pro forma event lasting about five days.

The pact is the first major labor settlement to occur since the Reagan administration took office. If it sets the pattern for other industries, the agreement could spell considerable trouble for the administration's goal of less inflation without a serious recession.

A coal strike of some duration was assured last Tuesday when contract talks broke down, upsetting the union's 10-day contract ratification schedule. The union's tradition is not to work without a ratified contract.

"It's a decent contract," union president Sam Church said yesterday morning after his meeting with the BCOA, the bargaining agent for 130 coal companies in the East and Midwest.

"We didn't get everything we wanted, but we got a good agreement. . . . I think our people will accept it," Church said.

The union leader and the BCOA's chief negotiator, B.R. (Bobby) Brown, refused yesterday to give details on the settlement before it was presented to the bargaining council. But some details leaked out.

Major issues and their likely resolutions include:

Total economic (pay and fringe) benefits. The union began by demanding a 51 percent increase. The BCOA countered with 19 percent, and the two sides settled on 36 percent, which is roughly in line with the union's recent settlements with western coal mine operators.

Cost-of-living allowance (COLA) tied to the consumer price index. The union forfeited this benefit in its 1978 contract, tried to reinstitute it this time, and failed.

Multi-employer pension plan. The industry said the existing plan was too costly, and larger BCOA firms pushed for company-by-company pension coverage so they would not be responsible for obligations of smaller firms that have gone out of business. But the union argued that the company-by-company approach would overburden remaining smaller firms and destabilize coverage for many of its members. The BCOA yielded on this.

Productivity. Faced with a declining share of domestic coal production, from 70 percent in 1970 to 44 percent in 1980, BCOA firms have been trying to increase productivity. Accordingly, the industry, representatives used this year's talks to push for mandatory overtime, Sunday work, and continuous mining operations -- most measures the union opposed.

"There will be no coal mining on Sundays, voluntary or otherwise, under the tentative agreement," a union source said yesterday. However, the source declined comment on the rest of the BCOA's productivity demands.

Other issues involved the fate of the arbitration review board, a court of last resort on grievances, which the union wanted to eliminate, and arrangements for royalty payments to the union's health and welfare funds from BCOA companies purchasing "nonsignatory" coal from firms not covered by the national agreement.

Union sources said yesterday that the ARB has been knocked out of the proposed agreement. An agreement was "worked out" on the nonsignatory coal, according to sources who would not give details on the compromise.

Church and his aides conceded yesterday that despite all of their rhetoric last last week about a new strike that could rival the record 111-day UMW walkout in 1977-1978, they wanted to keep this year's work stoppage as short as possible. The UMW has no strike fund, the industry has huge coal stockpiles and, despite their leaders' bravado, it was widely assumed that the miners would wind up with the largest lumps in an extended work stoppage.