Britain's bestknown national newspapers, the Times and The Sunday Times, which have been silenced by a labor dispute for more than three months, may resume publication April 17 under a surprise agreement reached here today by management and union leaders.

In marathon overnight meetings with the minister of employment, the unions agreed to negotiate on work rules and the introduction of new technology. Management agreed to reinstate with back pay 1,500 workers who had been laid off and to keep another 1,300 who would have been let go Friday.

Complicated negotiations on the substance of the dispute now must be completed by management and 34 different union bargaining units before publication can resume on the target date of April 17, but a Times management spokesman said today it was "almost inconceivable" that the newspapers would not reappear by then.

"There are provisions made all through this to make sure that these negotiations do not break down," he said. If all the issues are not resolved by April 7, he added, both sides have agreed to call in a professional conciliation service.

Complete reinstatement and full back pay for the laid-off workers depends on a final agreement being reached in time to resume publication by April 17.

"We are going to try very hard," said Marmaduke Hussey, managing director of the two newspapers. "And I'm convinced the union leaders are going to try very hard."

"We are not out of the woods yet," warned Joe Wade, general secretary of the National Graphical Association, the large printers' union that had refused to negotiate with management until reinstatement was agreed to and a date for resumption of publication we set.

Wade said the agreement to begin negotiations, which his union quickly approved today, "is a victory for common sense."

The Times management had shut down the two newspapers, as well as the Times Literary Supplement and the Times Educational Supplement, Nov. 30 after it failed to win agreement from all its unions on the introduction of computerized printing equipment, elimination through attrition of hundreds of workers, and an end to wildcat work distruptions that had plagued the newspapers and given The Sunday Times the sobriquet "The Sunday Sometimes."

Agreements had been reached with 20 of the 54 bargaining units at the newspapers, which kept 1,200 employes, including all reporters and editors, on the payroll and working even though nothing was being published. The rest of the workers were given notice that they would be laid off in stages ending Friday.

The apprach of Friday's final wave of layoffs, with the prospect that picketing would begin and animosities would worsen, had created a "now or never point" for negotiations, according to Employment Minister Albert Booth. After several days of behind-the-scenes approaches, he initiated and acted "as a go-between" in the talks that ended with today's 3 a.m. agreement.

Britain's Labor Party government has been anxious to help end the Times dispute, which had become a symbol of a long winter of labor disputes that embarrassed the government and hurt the Labor Party in public opinion polls.

Although it still prides itself on being Britain's newspaper of record -- and plans to publish a digest of news and obituaries it missed during the shutdown -- The Times' influence had faded somewhat and its circulation fallen under 300,000. The Sunday Times, however, has a separate staff and a circulation of 1.5 million.

The disappearance of the two papers had benefited the other "serious" national newspapers here -- the daily Guardian, the Sunday-only Observer, the daily and Sunday Telegraph and the Financial Times -- all of which picked up some of the Times' circulation and advertising.

The Observer, which had been in great financial difficulty before being bought by America's Atlantic Richfield Co. two years ago, has profited the most. Its circulation has increased from 700,000 to 1.2 million since The Sunday Times disappeared.