Labor Secretary Ray Marshall led the coal industry and striking United Mine Workers into round-the-clock bargaining yesterday in an attempt to settle the increasingly disruptive 73-day coal strike by sometime today.

"We obviously don't have long. This thing can't go on," said Marshall as negotiations resumed under White House auspices with no immediate signs of progress - raising prospects of a presidential back-to-work order under the Tatt-Hartley Act.

Marshall issued his two-day "timetable" for bargaining as President Carter ordered a state of emergency in Indiana and met with governors of 12 Midwestern and Mid-Atlantic states that have been hit hardest by coal shortages and resulting power cutbacks.

The governors quoted Carter as warning that there will be serious economic repercussions if the strike isn't settled soon and urging the states to take steps to cut coal consumption.

The impact of the strike is growing daily in these heavily coal-dependent regions, although administration officials say the strike-caused shortage cannot yet be described as a national emergency. With coal supplies down to about three weeks in some areas, nonessential power useage is being cut back and widespread job layoffs are being threatened in many states.

In Indiana, several colleges and public school systems planned to close down for extra days and the university of Notre Dame darkened its "golden dome" - the symbol of the university - for the first time ever.

The energy emergency Carter declared in Indiana will permit relaxation of air pollution standards there, and the burning of coal that would otherwise be too "dirty" to use. He issued a similar declaration for Ohio last Saturday.

Meanwhile, "Operation Chimney Sweep" continued in Indiana as a second convoy of trucks under state police and National Guard protection hauled 2,000 tons of coal to utility plants - some of them over a path of nails apparently spread by striking miners.

In Maryland, the Bethlehem Steel Corp, put plans in motion to cut back operations at its giant Sparrows Point plant in Baltimore, with the first 500 employes to be laid off Sunday or Monday.

And in Tennessee, the Tennessee Valley Authority asked its 2.5 million customers to cut their electricity 819,846usage 20 percent to help avoid layoffs of up to 150,000 industrial workers.

On Capitol Hill, Rep. Clarence J. Brown (R-Ohio) took a dim view of the domestic coal industry, which the administration has looked upon as the centerpiece of its whole energy policy and declared: "The Arabs are beginning to look pretty reliable."

The Carter administration has broad emergency powers to cope with the strike, ranging from sending the military to dig coal to handing out free firewood. But its strategy thus far has been to let the collective bargaining process work as it will, and to do what it can - admitting that it isn't much - to alleviate hardships and assure fair allocation of available coal supplies.

The administration has noted pointedly that it is up to the states to take most of the energy-saving steps the law allows, including cutting back on industrial as well as nonessential electricity usage.

But Carter's basic hands-off policy toward bargaining began to crack earlier this week as pressures for stronger executive action mounted. Late Tuesday, responding to rejection of a tentative settlement by the UMM's bargaining council and apparent refusal of the Bituminous Coal Operators Association to reopen negotiations voluntarily, Carter summoned both sides to the White House for a resumption of talks.

After briefly defying the summons, the BCOA - reportedly under heavy pressure from top-level industrial executives as well as angry administration officials - agreed reluctantly Wednesday to resume negotiating.

Ground rules for the new round of talks were laid at a White House session Wednesday night and full-scale bargaining resumed at 9:30 a.m. at the Labor Department under Marshall's leadership.

After a somewhat pessimistic assessment to reporters in early afternoon, Marshall last night issued a statement saying: "Face-to-face coal negotiations are continuing, which in itself must be considered a good sign.

However, noted that "many difficulties remain" and said he would keep the bargainers going "as long into the night as seems advisable." He said presidential aide Landon Butler UMW's bargaining council was ensconced in a room close by "to improve communications and eliminate delays."

This represented an attempt to involve the rebellious council members as closely as possible in the actual negotiations and avoid in repetition of their settlement repudiation last weekend. In a similar move Wednesday, UMW President Arnold Miller agreed to expand the seven-man bargaining team to include three council members, who are participating in the negotiations.

The council, whose approval is necessary before a contract can be submitted to the 160,000 strikers for ratification, went along with the proposed 37 per cent wage-and-benefit increase by 1981 but balked at penalties for wildcat strikes, health benefit cuts and other industry demands.

Resolution of these problems was proving "difficult," Marshall said after the morning session.

He said the two-day deadline for bargaining could be extended if a settlement was within reach but was needed to reflect the administration's "sense of urgency" about the strike. He did not spell out what the next step would be, but Carter said Tuesday 3 bargaining failure would lead to "stronger measures," such as seeking an injunction under Taft-Hartley to force the miners back to work for an 80-day cooling off period. Such orders have not been particularly effective in resoving coal strikes in the past.

Testifying before the House Commerce Committee yesterday, Energy Under Secretary John F. O'Leary said that administration experts did not consider the situation severe enough to recommend that the president declare a national emergency because of the strike-induced power shortages.

"That decision will be made at the appropriate time by the president when we sense the situation is very serious." O'Leary told the committee at a hurriedly called afternoon session.

Rep. John D. Dingell (D-Mich.), committee chairman, said the Department of Energy's plan to deal with the shortages "relies too much on the states and utilities."

O'Leary said that the DOE and other government officials meeting with state and utility officials are doing all they can, adding that the state governors "are coming to the point where they have begun to recognize the areas of criticality."

In recent days, senior administration officials have been saying privately that some of the state governors, such as Ohio's James Rhodes and Pennsylvania's Milton Shapp, were reluctant to take the political heat involved in ordering public utility commissions to curtail power to industrial users. The governors, they say, were hoping to shift the burden to the White House. "It has been a game of chicken," one top administration official said.

But, West Virginia, Indiana, and Rhodes' Ohio now have all declared states of emergency and are beginning to order industrial curtailments:

The Indiana Public Service Commission has called for a 30 percent cutback by industrial users whose supplying utilities have less than 40 days of coal on hand.

West Virginia has declared a state of emergency and is importing coal where possible. The Tennessee Valley Authority, which earlier had said it was going to begin curtailments, has told DOE officials it will begin March 1.

And the Ohio public utilities commission has ordered utilities to purchase as much power as possible from out of state. One utility system hard hit by the strike which serves parts of Ohio and West Virginia, the Allegency Power System, is now at 10 percent curtailment, and expects to go to 30 percent cutbacks next Monday.

Rep. Brown, whose state was severely affected by last winter's natural gas shortages, echoed earlier projections that as many as 700,000 Ohio workers could be forced off their jobs by the end of the month because of the coal strike. "The entire economy will grind to a stop without Ohio's glass and rubber production - especially the auto industry," the congressmen warned.

The Council of Economic Advisers and labor and Commerce Department experts, however, say that it is difficult to estimate how much unemployment will come from the strike.