Most of the nation's 160,000 striking coal miners returned to work yesterday despite sporadic picketing that kept some mines closed in the absence of strike settlement for union construction workers.

A government mine safety official estimated that 90 percent of the nation's mines were operating, and a spokesman for the Bituminous Coal Operators Association said only 19,000 miners stayed away from work because of construction workers' picketing.

The 110-day coal strike ended officially Saturday night when the United Mine Workers and the BCOA signed a new three-year contract governing the 160,000 miners, but the UMW and the Association of Bituminous Contractors still had not come to terms on a contract for 14,000 mine construction workers.

Construction contract bargainers were reported nearing a settlement late yesterday, but there was no word on when agreement might come. Three years ago, after a three-week UMW strike, it was two weeks before a construction contract was ratified and the mines could resume full production.

Union leaders had urged construction workers not to picket so that the miners, hard-pressed for cash after 16 weeks without pay or benefits, could return to work and collect a $100 bonus guaranteed by the new contract for workers who showed up on the first day of operations.

In most places this happened, but picketing turned away an estimated 8,100 miners in Illinois, 6,000 in northern West Virginia and Ohio, 2,6000 in Pennsylvania and hundreds scattered elsewhere in the Appalachian and midwestern coalfields.

Some non-BCOA mines also remained closed until the operators signed the industrywide contract. But UMW pensioners, who were dissatisfied with the contract's failure to equalize pension benefits between older and younger retirees, did not follow through on threats to picket the mines.

Miners traditionally refuse to work without a contract in hand or to cross a picket line under almost any circumstances.

There was some concern in industry circles that picketing would pick up today, now that the miners have pocketed their bonuses.

But utilities, railroads and other affected industries moved quickly to resume full operations in anticipation of plentiful coal supplies in the near future. Utilities dropped conservation measures, and laid-off workers were being called back.

Similarly, the Justice Department moved in U.S. District Court here to drop the Taft-Hartley Act procedures that President Carter invoked earlier this month during a stalemate in the negotiations to force the union to abandon its strike.

The strickers ignored the order, and U.S. District Court Judge Aubrey E. Robinson Jr. refused an extention on grounds that the government failed to prove that a national emergency existed and had not enforced the temporary order.

A hearing had been scheduled for today, however, on the government's request for a full 80-day Taft-Hartley injuction. The request had been made before the contract was negotiated and ratified.

The contract, approved by 7 percent of the strikers voting Friday after an earlier draft was rejected March 5, provides for a 39 percent increase in wages and benefits over three years. But miners' approval of the pact was grudging in many cases because it provides for company take-over of the union's previously independent health-care system, medical versial new production incentives and a continuation of pension inequities. Wildcat-strike penalties, a major reason the earlier contract was rejected, were dropped, however.

The construction workers' contract was believed to be taking shape along these same lines, with some posible differences, including wages.

John Guzek, chief UMW negotiator, said he believed the construction pickets would withdraw when a tentative contract is negotiated, although a ratification process of several days must follow.

Guzek expressed regret that some construction workers picketed the mines. "Due to the pickets, they [the miners] were deprived of getting the $100," he said.