Thousands of long-distance telephone callers encountered recorded apologies and delays of up to a minute in reaching operators yesterday on the first business day of the nationwide strike against American Telephone & Telegraph Co.

The company also was forced to shut down about half its factory production of telecommunications and computer equipment in 17 states.

With 38,000 telephone operators among the 155,000 striking members of the Communications Workers of America, AT&T's circuit boards were jammed during the peak Monday morning calling period as company supervisors donned headsets to temporarily replace strikers. "We had a level of service that was pretty good," said AT&T spokesman Herb Linnen, who said delays ranged from "a few seconds to up to a minute."

Most callers did not encounter delays because 90 percent of AT&T's average 33-million call daily volume are connected automatically without operators, who handle person-to-person, collect, emergency and billing problem calls. Callers seeking 411 directory assistance or making local calls were also not affected because local phone companies are no longer part of AT&T since the 1984 Bell System breakup.

No new formal negotiations were scheduled, but Kay McMurray, director of the Federal Mediation and Conciliation Service, met separately yesterday with officials of AT&T and CWA, and then scheduled a mediation session for last night, according to sources.

The strike, largest work stoppage in the nation since the 1983 AT&T strike by 500,000 CWA members, was caused primarily by disputes over wages, the proposed elimination of cost-of-living inflation adjustments and an AT&T plan to create a lower-paid category of skilled technicians, according to both sides.

AT&T was able to operate 13 of 25 manufacturing plants because those facilities are represented by a second union, the International Brotherhood of Electrical Workers, which has tentatively accepted a new three-year contract with the same terms the CWA rejected. Those terms include pay raises of 2 percent this year, 3 percent in each of the next two years -- with cost-of-living adjustments eliminated -- pension improvements and a job-security clause that expands union members' rights for transfers and retraining in event of impending layoffs.

CWA, citing AT&T's $2 billion profit in the last five quarters and substantial pay raises to management, has termed the wage offer inadequate.

AT&T, pointing to lower costs of its mostly nonunion high-tech competitors, has said larger pay raises would make its products too costly to compete.

Factory workers and several thousand operators belonging to IBEW reported to work yesterday. But at several AT&T sites in New England and the Midwest where both the IBEW and CWA represent employes, IBEW members in most cases refused to cross CWA picket lines and stayed out of work, according to officials of both unions.

The two sides appeared to make progress during yesterday's "Good Morning America" program on ABC. AT&T Executive Vice President Charles Marshall in New York said the company would not lay off skilled technicians, who earn $646 per week, and then rehire them into a new job category for "wire pullers" which would pay $360.

"Chuck, if that's the position of the company, we could settle that issue," CWA President Morton Bahr said in Washington. Bahr, who said AT&T did not make such assurances at the bargaining table, then spoke further to Marshall off the air from the ABC studios.