United Mine Workers members overwhelmingly rejected a negotiated settlement of the nation's 90-day-old coal strike yesterday as the Carter administration prepared to invoke antistrike provisions of the Taft-Hartley Act.

Administration officials said President Carter will act today to appoint a Taft-Hartley board of inquiry -- the first step toward obtaining a federal court injunction ordering the 160,000 rebellious strikers back to work for an 80-day cooling-off period.

An injunction could come within days, but there is no assurance that the miners, who defied their own leaders in rejecting the proposed contract and have previously ignored injunctions, would obey a back-to-work order.

In an attemp to make an injunction more palatable to the strikers, administration officials were making overtures to coal operators to raise wages considerably above the $7.80 average hourly rate the miners were receiving under their expired contract.

This was described as an alternative to legislation authorizing temporary government seizure of the mines, which sources said may still be pursued if an injunction fails to reopen enough mines to get coal moving to alleviate critical coal shortages in a number of Eastern and Midwestern states.

On the third day of coalfield voting, opponents of the contract were easily maintaining their earlier ratio of more than 2 to 1, defeating the proposed pact in virtually every district where more than fragmentary returns were available.

With 482 of the UMW's 794 locals reporting returns to the union's headquarters here, the vote was 44,666 against ratification and 19,885 for it, with the margin widening as returns from many big Appalachian locals poured in.

When the 2-to-1 lead was holding strong with 60 per cent of the vote tallied. UMW Secretary-Treasurer Willard A. Esselstyn appeared before reporters at the Mayflower Hotel press headquarters and gave what appeared to be a concession statement.

"It appears now that this contract isn't going to make it . . ." said Esselstyn, declining to elaborate further except to say that the turnout would be about 105,000, somewhat higher than earlier returns indicated.

Asked if the strikers would obey an injunction, Esselstyn shook his head and said, "I don't know."

As miners were voting, administration officials -- who orchestrated the settlement that the miners rejected --met throughout the day to try to map their way out of the coalfield briarpatch.

After a meeting with his top departmental advisers, Labor secretary Ray Marshall went to the White House for consultations with presidential aides and a meeting with Carter after the president returned from a weekend at Camp David.

There was no word on the outcome of the meeting between Carter and Marshall, but administration officials said earlier in the day that the first step would be to invoke emergency provisions of the Taft-Hartley Act for the first time in seven years.

The Associated Press reported that the administration already had lined up three members for the board of inquiry: Carl Warrens of the University of Louisville in Kentucky; Eva Robbins, a labor arbitrator from New York; and Jack Gentry, a Washington lawyer.

White House press secretary Jody Powell told reporters before the Carter-Marshall meeting: "It's clear from the trend in the voting that the president will have to act no later than tomorrow. It will be the primary topic of the Cabinet meeting tomorrow (Monday), to be followed by a bipartisan meeting of the congressional leadership."

A Labor Department source said innovocation of the Taft-Hartley Act would be tantamount to calling an impasse in the industrywide negotiations between the UMW national leadership and the Bituminous Coal Operators Association, opening the way for company-by-company or regional bargaining.

This could have devastating consequences for the once proud and powerful UMW, which is already in a state of virtual anarchy and open rebellion against its president, Arnold Miller. It could also raise serious questions about restoration of miners' benefits one of the principal union bargaining goals, and about labor stability in the coalfields, the industry's chief aim in the negotiations.

The contract, accepted by the BCOA 10 days ago under intense White House pressure to agree to anything the UMW leadership could swallow, provided for a 37 percent increase over three years, one of the biggest economic gains for a major union since the UMW's 56 percent increase in 1974. It would also guarantee payment of medical and pension benefits, which are now dependent on production royalties and have been suspended.

But it also includes some of the industry's labor-stabilizing and cost-controlling demands that raised a cry of outrage throughout the coalfields: disciplinary action against wildcat strike leaders, deductibles of up to $700 a year per family for health care that was previously free (although intermittent), absenteeism controls, a continuation of the disparity between pensions for older retirees and more recent ones and company takeover of the union's trustee-run health-care system.

The miners' vote represented a major setback for the administration after initial hopes it had weathered the coal crises with last month's negotiated settlement, and officials did not appear optimistic yesterday that Taft-Hartley would provide any instant successes.

The Taft-Hartley Act has been used 34 times since it was passed in 1947, most recently by President Nixon in a dockworkers' dispute in 1971. Injunctions have been requested in 29 of the 34 cases and denied only once, when Nixon sought a back-to-work order against 200 Chicago elevator employees.

According to Labor Department statistics, injunctions have succeeded in halting strikes in all but one case: the 1949-50 coal strike that was settled only after President Truman asked Congress to authorize the government to temporarily seize the mines.

This is how emergency provisions of the Taft-Hartley Act operate:

After finding that a strike threatens to "imperil the national health and safety," the president appoints a fact-finding board of inquiry, usually composed of three members, and gives it a deadline -- anywhere from days to weeks -- for reporting.

The president, after receiving the report, may direct the attorney general to ask any U.S. District Court judge for an injunction ordering the strikers back to work for 80 days.

Negotiations would then be resumed under federal mediators. After 60 days from issuance of the injunction, the board of inquiry files another report including the industry's last contract offer.

If the final offer is accepted in a rank-and-file referendum, the strike is over. If it is rejected, the injunction is lifted and the miners are free to go back on strike.

Emergency provisions of the Taft-Hartley Act were used three times in coal disputes, all during the Truman administration. In a 1958 dispute, miners defied a temporary restraining order, resulting in contempt-of-court fines of $20,000 against former UMW President John L. Lewis and $1.4 million against the union, but went back to work after an 80-day injunction was imposed under Taft-Hartley. When another Taft-Hartley injunction was issued in 1950, the miners defied it and only returned to work after Truman threatened to seize the mines.