The possibility of a wildcat Metro strike this summer apparently was averted yesterday when an arbitration panel ruled that Metro must pay a $7.6 million cost-of-living increase to its transit workers beginning July 1.

Richard S. Page, Metro's general manager, announced moments after the decision was released that "We will make the payment." Metro had sought to delay paying the increase in hopes the amount would be reduced in a new contract still under arbitration.

When Charles Boswell, president of Local 689 of the Amalgamated Transit Union, was asked if there was now any likelihood of a strike, he said: "Absolutely not."

Page had predicted publicly and union officials had privately agreed that, if Metro had forestalled the cost-of-living increase, would have been possible or even probable. The transit union, which represents 5,000 bus drivers, train operators, station attendants, mechanics and clerks, is forbidden by federal law from striking Metro. That fact has not prevented wildcat strikes in the past.

Metro's contract with the union expired April 30 after union and Metro negotiators had been unable to resolve a number of differences. Under the federal law that permitted Metro's takeover of four failing bus companies in 1973, unresolved contractual issues must go to binding arbitration.

The transit union contract that expired April 30 contained a clause stating that "all the conditions in this contract shall remain undisturbed during the arbitration proceedings." One of those conditions is the requirement that, four times a year, Metro must increase the salaries of its transit workers by the same percentage that the Consumer Price Index for the District of Columbia area increases.

That contractual clause, a holdover from the last contract that the old D.C. Transit System Inc. negotiated with Local 689 late in 1972, has given Metro's transit workers better protection against inflation than that received by other public employes in the Washington area.

The result has been increasing political pressure on Metro from the local governments that subsidize its budget to control labor costs. The issue has become particularly heated in recent months with inflation hitting 18 percent.

Metro argued, in seeking to delay the July payment until the new contract is settled, that it was probable there would be a reduction in the cost-of-living protection in the new contract. Therefore, if Metro paid on the basis of the old contract in July, it would probably overpay and would have trouble recouping the money.

Richard I. Bloch, the neutral member of the arbitration panel, said in his ruling requiring the July payment that "the terms of this labor agreement, including those requiring extension of its provisions beyond the expiration date, apply without regard to the odds they will be changed."

A final new agreement is not expected from another arbitration panel before the fall.

Metro officials estimate that the July payment will cost $7.6 million. If there is still no new contract in September, when the next payment is due, the cost will be another $3 million. Metro's budget for the fiscal year beginning July 1 will already be out of balance with those high increases. The most recent cost-of-living increase at Metro, which started in March, was 26 cents an hour for a fully qualified bus driver. That raised the driver's hourly pay to $9.86, or $20,509 a year excluding overtime, which almost all drivers receive in some measure.

Depending on where the Consumer Price Index falls, the July payment could be in the range of 50 cents an hour, Metro officials estimate.

Metro has argued that federally required binding arbitration, plus the cost-of-living escalator, plus the "undisturbed clause give the union every reason to delay and to refuse to negotiate.

In an interview in January, Walter Bierwagen, international vice president of the Amalgamated Transit Union, all but agreed. "I think in most instances we come out well in arbitration," he said. ". . .I can't think of anything significant we've won out of a strike situation."