The United Mine Workers union and the Bituminious Coal Operators Association reached a tentative agreement early this morning that could end a 63-day national miners' strike.

"We finally made it," said UNW President Sam Church Jr., as he emerged at 1 a.m. from talks at the Capital Hilton Hotel where he, his aides and BCOA negotiators had been meeting off and on since 9:30 a.m. yesterday.

"We have a contract. . . . It's better than the last contract, it's better," Church said.

Church was referring not to the union's three-year contract that expired March 27, precipitating the latest in a series of triennial UMW strikes, but instead to another tentative agreement reached March 23.

That pact was rejected by more than 2 to 1 in voting by the union's 160,000 members.

Despite Church's optimism today, there is no firm reason to believe that this second tentative agreement will escape a similar fate.

The new agreement's first test comes later today before the UMW's 39-member bargaining council, which has been meeting here since last week.

If the bargaining council approves the proposal, the rank and file, mostly in the East and Midwest, will have 10 days to reject or accept it.

Thus, this latest UMW strike, which has cut domestic coal production from an average of 16 million tons weekly to about 8.5 million tons, could become a 73-day walkout. The union's last strike, in 1977-1978, lasted 111 days.

The miners rejected the last proposed pact largely because they believed it undermined union security in BCOA mines and jeopardized their jobs. The BCOA represents 130 soft-coal producers.

The rejected agreement allowed BCOA firms to discontinue royalty payments to the union health-and-welfare funds on supplemental coal purchased from mines not covered by a BCOA-UMW agreement. It also allowed the covered companies to employ non-union subcontractors in certain cases, a provision that greatly angered the rank and file.

Church said this morning that "no problem" remains on either issue. He did not elaborate.

The overall economic impact of the current strike is not clear.

For example, although domestic coal production has cut in half, electric utilities nationally had consumed only 5.1 percent of the 174.8 million tons of coal they had stockpiled above ground since March 27, according to figures provided by the Department of Energy.

In the East, most immediately affected by the strike, electric companies had used 10.8 percent of their available coal, compared to 8.2 percent used by power companies in the Midwest, according to DOE.