Government and union negotiators recess talks last night after 10 hours but agreed to meet again today in an attempt to reach an agreement in principle on a new contract in time to avert a nationwide air traffic controllers' strike threatened for Monday morning.

"I don't want to make anyone overly optimistic," Transportation Secretary Drew Lewis said last night when the talks ended. He said each side would spend the morning separately going over proposals that were put on the table yesterday and would get back together at 2 p.m. today.

"We really hope that we can work something out so that there will be no strike," Lewis said. He said the negotiators are still working within the $40 million total package offered earlier by the government but are trying to restructure it to avoid an inflatinary impact on the economy while satisfying the economic demands of the air traffic controllers.

Robert E. Poli, president of the Professional Air Traffic Controllers Organization initially said at the conclusion of last night's meeting that no progress had been made in yesterday's talks. He later explained that "no progress" meant that "we don't have a settlement."

"We'll be back tomorrow," Poli said.

Yesterday's talks began when Lewis met with Poli for 45 minutes in the morning, then turned the talks over to the Federal Aviation Administration bargaining team. The discussions took place at the offices of the Federal Mediation and Conciliation Service with the assistance of federal mediator Kenneth Moffett.

Although Lewis worked throughout the day for a settlement, he maintained his position that if a strike occurs, the government will immediately seek fines and other penalties against the controllers.

Poli originally had threatened to poll his membership for a strike if there was no contract settlement by 11:59 p.m. tonight; a strike decision could affect the 7 a.m. shift tomorrow. Pressed by members of Congress Friday, however, Poli said he would delay a walkout if "meaningful" talks were continuing and an agreement appeared possible.

A strike, which would viloate federal law and a permanent injunction specifically barring a PATCO strike, could cripple most of the nation's commercial air service, setting in motion an FAA contingency plan sharply reducing the airlines' 14,000 daily scheduled flights. Most flights under 500 miles would be grounded.

PATCO represents about 14,8000 of the nation's 17,000 controllers. In the event of a strike, the remaining flights would be handled by nonunion controllers, union controllers who don't strike and about 3.000 supervisory personnel.

There were vast differences in the bargaining positions when the two sides began talking yesterday. In contrast to the government's $40 million annual price tag on a new four-year contract, PATCO's package would cost the government $770 million a year. PATCO was seeking an across-the-board increase of $10,000 in the annual pay of the controllers, whose salaries now range from $20,000 to $50,000; a reduction of the work week from 40 to 32 hours; improved pension benefits, and a voice in FAA policy changes in controller procedures.

The government's proposal included a 10 percent pay raise for controllers who act as on-the-job training instructors; an increase in pay differential for controllers who work at night from 10 to 20 percent; a guaranteed half-hour lunch period or the equivalent in overtime pay; payment of a year's severance to five-year veterans at the busiest stations who are forced to retire for medical reasons; and an opportunity for PATCO members to sit on committees that recommend changes in FAA controller procedures.