Just as the nationwide strike against American Telephone & Telegraph Co. began yesterday at 12:01 a.m., a one-on-one private meeting took place between AT&T's top labor-relations executive, Raymond E. Williams, and his old friend and adversary, Morton Bahr, president of the 600,000-member Communications Workers of America.

With several billion dollars at stake, the two men, longtime opponents across the Bell System bargaining table, met alone in Bahr's Washington union office for some old-fashioned horse-trading. They were trying to cut a deal to settle a new contract for 155,000 AT&T long-distance operators, clerical workers, factory workers and technicians who make, install and repair telecommunications and computer equipment.

But the two tough-talking New Yorkers, veterans of AT&T's longest and most bitter strike in 1971 and another in 1983, broke off the late-night talk within 15 minutes. Bahr wanted more money and job security for workers, and Williams, a former union member, wanted to control costs to keep AT&T competitive. Unable to resolve complex disputes over cost-of-living allowances, new job classifications, technology and job security, they parted company. The strike was on.

Times have changed for AT&T and the CWA in the new hypercompetitive "Information Age." New problems raised since the 1984 breakup of the old Bell System were too complex to be resolved in an old-style last-minute deal. AT&T has giant new competitors, new pressures from Wall Street, a new chief executive who took office yesterday, and a new "hard bargaining" position in dealing with the CWA, the world's largest telecommunication union, which is trying to assert itself and grow in new high-tech industries.

Most telephone customers will feel little immediate impact because 90 percent of the 33 million daily calls in the automated long-distance network are handled by digital machines, not human operators, who assist only on person-to-person, collect calls, and emergencies.

Local phone service, including directory assistance and local repairs, is also not affected by the strike because the 1984 Bell System breakup split off the local telephone monopolies such as the Chesapeake and Potomac Telephone companies. C&P's parent firm, Bell Atlantic, and the seven other regional "Baby Bell" firms will bargain separate CWA contracts when their current labor agreements expire Aug. 9.

Callers who needed an AT&T operator yesterday encountered recorded apologies for strike-related delays, as supervisors staffed phone lines, planning to work 12-hour shifts and six-day weeks.

Negotiations resumed briefly yesterday afternoon at the Washington Hilton, but broke off indefinitely.

"This strike has taken place for one reason. The company is seeking unwarranted concessions that cannot be justified," Bahr said at a news conference yesterday, referring to AT&T demands to eliminate cost-of-living adjustments, end bonus pay for workers who meet production quotas, and create lower-wage job categories for some technicians.

"We will not engage in concessionary bargaining with a company that is healthy, that is earning enormous profits . . . and that has remained successful on the fruits of the labor of our members," Bahr said, adding, "We can afford to stay on strike a lot longer than they can."

AT&T spokesman Herbert Linnen disputed Bahr's assertions, saying, "We did not ask for concessions. We did not ask for givebacks." He said AT&T's smaller union, the International Brotherhood of Electrical Workers, which represents 41,000 employes, has tentatively accepted the same package offered to the CWA; the package includes an 8 percent pay raise over three years, pension improvements, and strengthened job-security language.

IBEW officials were not available for comment, but a recorded announcement said the union is not on strike at AT&T and will present the company offer to a membership vote by June 10.

The IBEW represents workers at 13 of AT&T's 24 manufacturing plants in 17 states, and AT&T said it expects to operate those plants, and will attempt to operate others using supervisors. Bahr said he expects the IBEW to honor picket lines and refuse to work at other plants where CWA strikers are also employed.

AT&T supervisors -- the phone company has historically been regarded as top-heavy with management and has some 115,000 managerial personnel -- will staff nine large regional sales and service centers, many of the 700 AT&T Phone Centers, and switchboards.

While immediate consumer impact is limited, the AT&T strike is expected to have substantial effects on other fronts, especially if it is prolonged.

American Telephone & Telegraph is the major supplier of complex telecommunications switching equipment for the regional telephone companies, and is also a major provider of computers, office-automation and telephone switchboards for thousands of business and government clients. Those customers may have delays and could take their business elsewhere, industry analysts say.

Job security has been a major issue because AT&T has cut 56,000 jobs and laid off 15,000 workers since divestiture, and the union fears more reductions. Union members overwhelmingly authorized a strike two weeks ago if AT&T did not move toward the CWA goal of career job security.

Average salaries at AT&T range from about $21,300 a year for operators to $31,700 for skilled technicians. AT&T initially offered pay raises totaling 5 percent over three years, but increased the offer to 8 percent -- with no cost-of-living protection.

The company earned $2 billion in profit in its last five quarters and gave a 33 percent pay raise to its outgoing chief, Charles L. Brown, fueling CWA demands for larger pay raises. But AT&T, citing lower wages of nonunion competitors, wants to cut costs.

A major push by the company is to create a new lower-paid job title for technicians who perform less-skilled work. But the CWA fears that AT&T would be able to continue laying off its $31,000-a-year technicians, while assigning those duties to lower-paid workers.

The new chief executive of AT&T, James E. Olson, "is going to get tough. They have to get tough with the union . . . . They say they want to be the next IBM, but they won't get there unless they get their costs down," said Glenn Pafumi, an AT&T analyst with Dean Witter Reynolds. "The company has competitors now and they can't afford to be soft with the union the way they were before competition."