NBC and union negotiators representing 2,800 producers, writers and technicians on strike against the network for the past nine weeks broke off contract negotiations last night, government mediators said.

"We've met with both parties all day and into the evening ... and we were not able to resolve the dispute," said Gayle Wineriter of the Federal Mediation and Conciliation Service.

Wineriter said the agency would remain in contact with the network and the National Association of Broadcast Employees and Technicians, but he was not optimistic that any end to the strike was near. "If it appears that anything can be done, we'll get them back together," he said.

NABET officials blamed NBC negotiators for breaking off the bargaining, saying they walked out of a bargaining session here shortly before 9 p.m. after the union rejected the company's demand for contract language allowing it to use more nonunion workers for covering sports and news events.

"We estimate that would have cost our members a minimum of 150 jobs, and we could not compromise on anything like that," said John Krieger, a NABET spokesman.

McClain Ramsey, a spokeswoman at NBC's headquarters in New York, quoted negotiators for the network as saying the union was offering "old wine in new bottles" and had not shown a willingness to compromise on the significant issues keeping the two sides apart.

"We certainly went into those negotiations with good faith, as we have with all negotiations, and hoped to find an agreement," she said. "Nobody would like to see a settlement more than NBC. We didn't call the strike."

The strike began June 29 when NBC workers rejected the company's last offer for a new accord to replace a contract that had expired March 31.

Largely at the urging of the Roman Catholic Church, the two sides sat down at the bargaining table under the auspices of federal mediators on Aug. 25 following a month-long hiatus in the bargaining.

Cardinal John J. O'Connor of New York, who earlier had refused to allow nonstriking NBC crews into his home, won an agreement from the network to attempt another round of bargaining in a meeting Aug. 20 at his residence with NBC President Robert Wright and Thomas Donahue, secretary-treasurer of the AFL-CIO.

"We went through a very laborious process of explaining our objections to their last offer and giving the company a lot of information on how conciliatory we were, even making concessions on the daily-hires issue," Krieger said last night.

"They agreed to some minor modifications," he added, "but they were still portraying very rigid positions, saying they would walk out if the union did not agree to its programs."

The network has contended it needs more flexibility in using part-time free-lance workers, citing a study by a hired management consultant that it has more full-time employes than it needs and that their time is often wasted.

According to NBC executives, producers, writers, camera operators and sound technicians on strike earn more than $100,000 a year, including overtime.

Union officials had conceded that some members covering intensive news developments at the White House and on other high-profile assignments do make that much. But they said the base pay for a typical sound technician is in the range of $850 a week.