Rank-and-file members of the United Mine Workers yesterday ratified a new soft-coal contact, ending a 73-day-old-strike that had cut coal production in half and was beginning to eat into electric utility stockpiles.

With 85 percent of the vote in last night, the contract with the Bituminious Coal Operators Association was passing by a more than 2-to-1 ratio with 57,210 miners, 69 percent, approving the agreement and 25,798, 31 percent, voting against it.

That was a turnabout from what happened March 31 when UMW members voted 2 to 1 to reject a tentative agreement designed to replace a three-year pact that expired March 27, precipitating the strike.

Yesterday's ratification means that most of the 160,000 striking miners will return to work will receive a $150 bonus under the terms of the new agreement that was signed here at 10:45 lst night at UMW headquarters.

UMW President Sam Church Jr. predicted that the ratified agreement would be "the best contract negotiated by union and industry this year."

Fter signing for the coal industry, Joseph Brennan, president of the BCOA, declared: "Labor and management will continue to work together to make coal the center piece of our nation's energy policy."

LUMW safety committees began touring the shut-down mines early today, checking for gas leaks, weakened mine support structures and other possible safety problems that may have developed while the mines were idle.

The safety checks are supposed to be completed by the time the first shift begins tomorrow, according to UMW spokesman Eldon Callen.

Church "is very concerned that the mines be run safely and that the miners be careful in returning to work," Callen said yesterday.

"People lose fomw of their coordination after being away from the mines for that length of tine. So, they have to work a little slower, more carefully," when they return to work after a long walkout, Callen said.

However, despite those words of concern, there was jubilation at UMW headquarters as the vote tallies from the soft-coal fields in the East and Midwest poured in, confirming Church's statement in Wilkes Barre, Pa., earlier yesterday that this latest tentative agreement would be ratified by his general membership and would be in effect today.

The union leaders particularly were heartened by their ability to reserve the setbacks they suffered two months ago in UMW districts 17 and 9 in West Virginia -- two major union divisions where the first contract went down by as much as 89 percent and 76 percent respectively. Yesterday, District 17 miners gave the new contract 57 percent approval and voters in District 29 favored it by 29 percent.

The major fators in the turnabout seemed to be the inclusion of a provision that will require the 130 BOCA member firms to continue royalty payments to UMW heatlh and welfare funds whenever the firms purchase coal from companies not covered by the BOCA/UMW aggreement.

The rejected pact allowed the coal companies to discontinue those payments, a provision which embittered mine workers who claimed that the elimination of royalties would lead to increased purchases of non-union coal.

Also, the new agreement tightens language concerning the use of non-union subcontractors involved in mine repair and other ancillary mine work. The rejected contract allowed mining companies to choose any subcontractor without regard to the subcontracting firm's union status.

Under the terms of the contract ratified yesterday, BOCA companies will have to first use their own active or laid off employees -- nearly all of whom are UMW members -- before they submit work bids to subcontractors.

Last night, Church said that something will have to be done to change the UMW ratification process in order to avoid any more lengthy strikes. Such changes -- for example, implementing selective strikes and doing sway with the union's traditional across-the-board "no contract, no work" rule -- could come at the next UMW constitutional convention in 1982, Church said.

He said that any amendments to the current ratification process necessarily would involve gret debate. The lst UMW walkout, in 1977-78, lasted 111 days.

The economic impact of the strike virtually was negligable during the first weeks of the walkout but became more evident as railroads and other coal-related operations began to lay off employes.

According to a spokesman for the National Coal Association, coal production dropped from a weekly average of about 16 million tons to about eight million tons during the dispute. The price of coal rose rapidly on the stock market as electric utilities began to comsume more of their large coal stockpiles that existed at the beginning of the strike.