Over protests from the United Mine Workers that use of the Traft-Hartley Act is an "outrage," a presidential board of inquiry cleared the way yesterday for the administration to seek an injunction today against continuation of the 93-day coal strike.

The three-member board heard 50 witnesses in six hours of hearings and then said it would have a report on the coal dispute to the president by noon today.

A Labor Department spokesman said plans call for the Justice Department to seek a temporary restraining order, the first legal step toward an 80-day Taft-Hartley injunction, in U.S. District Court here later in the day.

While the law does not empower the board to make recommendations, board chairman John N. Gentry said he agreed with President Carter that a bargaining impasse existed, and member Eva Robins concurred. The third member, Carl A. Warns, reserved judgment.

It will be up to the court to decide whether a national emrgency is threatened, as required by the act for an injunction. An injunction has been denied only once in 35 presidential requests for court back-to-work orders.

A Defense Department spokesman said the Pentagon has subnitted an affidavit contending that a continuation of the strike would adversely affect national security. Other executive departments are expected to be submitting similar statements to the court.

UMW officials predicted wholesale defiance of an injunction, despite risk of heavy fines and jail for union leaders who refuse to obey, and the White House toned down its earlier effort to convince the strikers that temporary government seizure of the mines was no longer an option.

"If at some point down the road the situations change, then the plans would change . . ." said White House press secretary Jody Powell. Powell's comments came after special trade negotiator Robert S. Strauss conceded Tuesday that seizure - which many miners want - was still a possibility.

During yesterday's hearings, held behind closed doors at the Federal Mediation and Conciliation Service offices under tight security, the UMW attacked Taft-Hartley while the Bituminous Coal Operators Association attacked the union and implied that the administration, at least until now, had been too deferential toward it.

Neither side held out high hopes for compliance.

"If an injunction issues, you will be unleashing upon the coalfields such fraternal and internecine strife as this nation has not seen since the Civil War," said Floyd Lamb, UMW Executive Board member from Ohio. "Union brother will be set against union brother. There will be more blood on the coal than is usual."

Nicholas Camicia, chairman of the Pittston (Coal) Co. and head of BCOA's last bargaining team, indicated that he was not confident that an injunction would be obeyed. "There's a lot of doubt," he said.

As for Strauss' suggestion that seizure may still be employed, Camicia said, it's a very bad statement. It just gives encouragement to the union not to go back to work under Taft-Hartley when they have seizure to look forward to."

In testimony before the presidential board, UMW Vice President Sam Church Jr. said it would be an "outrage to adopt the one-sided approach of the Taft-Hartley law" when the government could overcome coal shortages by reducing exports, doing more to reallocate coal among utilities and, "if necessary," seizing the mines.

Church quoted government reports to the effect that nearly 3 million tons of coal were exported between Dec. 9 and Feb. 18 and that steel industry stockpiles of coal were sufficiently large on Feb. 25 to last 39 days, more than the 34-day supply the industry had at the start of the three-week 1974 strike.

"If there were a shortage of metallurgical coal for the steel companies, this strike would have been settled weeks ago . . . The Steel industry - and its captive coal mines - seem to dominate the BCOA, and may, in large part, be responsible for the length of this strike," Church said.

Utilities are receiving more than half their normal coal deliveries, and will be using 25 per cent less coal as spring arrives, said Church, so "there is thus no 'national' shortage of coal, only an allocation problem."

BCOA, represented by its president, Joseph P. Brennan, said it regretted that "judicial intervention may be necessitated" but would obey any court order to reopen the mines.

"The efforts of the administration to bring an end to this dispute have been heavily directed toward industry; these efforts must now be directed to the true source of the dispute - the union and its membership," the association said, without going so far as to endorse use of Taft-Hartley.

Asked by reporters if Taft-Hartley would work in getting miners back to work, UMW President Arnold Miller told reporters: "No . . . it never has." Asked if he would obey the injunction, he said, "I've always been a law-abiding citizen . . .I suspect I always will be."

The board also heard a replay of the strike dispute from both sides.

BCOA testified that it needed wildcat strike controls - which many miners cited as a major reason they rejected the proposed strike settlement last weekend - to combat a workstoppage record "unparalleled in labor relations in the United States" and to reverse the industry's "continuing decline in productivity.

That association said that, over the past three years, the industry and its workers lost 6 million production days, 62 million tons of coal, $350 million in wages and $112 million in benefit fund royalties because of wildcat strikes. In the past eight years, he said, output per man-hour has dropped 50 per cent and labor costs per ton have tripled. Coal miners, it added, ranked "at the very top of the industrial wage scale" at the end of 1976.

The UMW's international officers said the dispute could be resolved by restoration of full benefits without proposed deductibles, increased pensions for older retirees, arbitration of proposed penalties for causing wildcat strikes and more flexibility in scheduling days off.

But the list from West Virginia Districts 17 and 19 was longer, including a limited right to strike over local grievances, elimination of wildcat strike penalties, unlimited cost of living increases and no more compulsory overtime work.