Rep. William Clay (D-Mo.), chairman of the House subcommittee on postal operations and services, yesterday accused Postmaster General William F. Bolger of attempting to bust four unions representing about 578,000 U.S. Postal Service workers.

Clay's attack was triggered by Bolger's efforts to get the National Labor Relations Board to define the "appropriate" bargaining structure under which USPS labor negotiations could take place. Bolger has contended that the current structure, under which the unions could bargain independently of one another, is "unworkable."

The talks, the largest labor-management negotiations this year in terms of workers represented, were scheduled to begin April 22. But Bulger's petition, which was filed April 17 and rejected nearly two weeks later by a regional NLRB office, has delayed collective bargaining to replace the current agreement that expires July 20.

"I think Bolger's filing of that petition was disruptive and potentially chaotic," Clay said in an interview yesterday. "It's an attempt at union busting. . . It can only cause the bargaining process to become more severe."

Clay labeled as "idiotic" Bolger's announcement Monday that he had asked the NLRB to extend by five days the deadline for appealing the regional labor board ruling. The deadline was yesterday, but the extension was granted late yesterday afternoon.

Bolger, in Portland, Ore., yesterday to attend a postal meeting, could not be reached for comment on Clay's charges.

Spokesmen for the American Postal Workers Union and the National Association of Letter Carriers, two of the largest unions representing USPS employes, said yesterday that they were confused by Bolger's latest move.