Labor Secretary Ray Marshall warned yesterday that the government will be prepared to act "immediately" to end the 12-week coal strike if miners reject a proposed settlement in secret-ballot voting this weekend.

He said chances of resuming negotiations in such circumstances are "very slight," and hinted broadly that rejection would be followed swiftly by a request for a back-to-work injunction under the Taft-Hartley Act -- perhaps coupled with temporary government seizure of the mines.

"We will be prepared to do something as early as Monday," Marshall told his first news conferencce since coal operators and the United Mine Workers reached a tentative agreement Friday under White House threats of both injunction and seizure.

"The same options as we had before are still there," he added, although he later said the administration's plan will reflect consultations with Congress, implying that some change is possible.

Last week congressional leaders of both parties signaled that they would respond quickly to a presidential request for authority to seize the mines, but that was before the Bituminous Coal Operators Association capitulated to government pressure to accept the UMW's so-called "bottom-line" demands.

Marshall conceded yesterday that rejection of the pact by the union's 160,000 striking members might weaken support for seizure, which is generally viewed as more anti-industry than anti-union. Other sources suggested, however, that seizure legislation could be written to crack down as heavily on workers as on their bosses.

Noting that there is "considerable ferment out there" over the contract, Marshall declined to predict the outcome of the voting by rank-and-file miners, some of whom were burning copies of the proposal and otherwise protesting its provisions during meetings throughout the coal fields yesterday.

Opposition appeared to center on newly proposed health care deductibles of up to $700 a year, disciplinary action against wildcat strike leaders and continued pension benefit disparities. Contract proponents were counting on an extensive selling job -- including radio ads by country music star Johnny ("Take This Job and Shove It") Paycheck -- to build a groundswell over the next two days for the contract's offer of benefit guarantees and a 37 percent wage-and-benefit increase over the next three years.

Apprehensive that government pressure could create a backlash among the independent-minded miners, Marshall said the administration would not attempt to sell the contract. But he then listed the contract's strong points, and said, "We know it's better than anything that we're likely to be able to do [for the minors] in the immediate future."

While Marshall did not rule out a resumption of talks, saying "you can never say 'never' in this business," he said talking has just about run its course. "It is clear that we gave the collective bargaining process one big push last week to try to get the settlement," he said. "I think it would be very difficult to get the negotiations going again."

Marshall said the Labor Department already has affidavits attending to a national emergency, as required to seek a Taft-Hartley injunction to end the strike for 80 days, and is proceeding on the assumption that the miners would obey a back-to-work order -- something they have not done in the past.

But he said Taft-Hartley is unlikely to be used alone, implying a combination of one or more of the three basic options: an injunction, seizure or binding arbitration. Seizure and arbitration would require congressional authorization; an injunction would not.

He said an impasse in industry-wide bargaining could also be declared, opening the way for company-by-company settlements, but indicated that this might not happen until after a board of inquiry, in the first step under the complicated Taft-Hartley process, makes its findings.

In what appeared to be a not soveiled hint to the miners, he said refusal to work under an injunction would mean "serious implications for food stamps. . . and a lot of other things" that the miners are relying on to last out the strike.