Leaders of the nation's largest postal unions said yesterday they are willing to continue bargaining beyond the July 20 deadline if their trouble-plagued talks with the U.S. Postal Service pick up speed and start moving toward a settlement.

Absolutely no progress has been made in the talks, though, union leders said. They accused Postmaster General William F. Bolger of attempting to provike a strike.

"For all intents and purposes, there have been no negotiations," said Morris (Moe) Biller, president of the American Postal Workers Union. USPS has made no wage offer, nor has it made "any meaningful counterproposal on any of the nonwage items" put forward by the APWU and the National Association of Letter Carriers, Biller said.

Those unions represent about 500,000 of the nearly 600,000 unionized postal employes and are bargaining jointly with USPS. Two other unions, the Mail Handlers and the National Rural Letter Carriers Association, are engaged in separate talks with postal officials.

Biller and NALC President Vincent R. Sombrotto said in interviews and at a news conference yesterday that they are prepared to call a strike -- despite legal prohibitions against walkouts by federal workers -- when their current three-year contract expires at midnight July 20. But both men said they would continue bargaining if "there is a chance of a contract settlemen" evident as the deadline passes.

"We ought to know 24 hours before the deadline, from USPS, if there is a chance of a settlement," Biller said.

Biller and Sombrotto accused Bolger of deliberately trying to provoke a strike. They pointed to the post-master general's unsuccessful legal maneuverings before the National Labor Relations Board, in search of the appropriate bargaining structure, which delayed the start of negotiations seven weeks. And they said USPS negotiators have met with union representatives for only about 2 1/2 hours a day, usually Monday through Thursday, since negotiations began June 16.

"If the Postal Service continues to treat the collective bargaining process as a sham . . . continues on its course of contemptuous behavior, then the only rational conclusion that can be drawn is that the post-master general is determine to provoke a strike, Sombrotto said.

"That's patently absurd," said Bolger spokesman. "The Postmaster General believes there are ways of peaceably solving this problem if we don't get an agreement by the deadline," such as going into fact-finding and binding arbitration, the spokesman said. However, in memos sent to his workers Friday in pay envelopes, Bolger threatened to fire any employe who walks off the job or deliberately obstructs mail processing and delivery.

Postal officials confirm they have yet to make an offer countering the unions' demand for a nearly 50 percent pay increase over the next three years, a demand Bolger has called inflationary and unrealistic.On other matters, such as health, safety and benefits, progress has been delayed because the unions "have put too many things on the table without any priorities," a postal management source said.

Meeting all of the unions' wage and other demands could increase the cost of the current 18-cent postage stamp to 45 cents by 1984.