The Reagan administration yesterday threw another roadblock in the way of the U.S. Postal Service's controversial nine-digit ZIP code, saying it wasn't satisfied that the longer ZIP would save money.

The Office of Management and Budget, acting under broad new anti-regulatory authority granted it in a Feb. 17 executive order, told Postmaster General William F. Bolger late last week that he was not to publish as final any regulations regarding the code. The Postal Service had planned to publish notice of the rules in Monday's Federal Register.

OMB already had requested, and received, a cost-benefit analysis on the proposed nine-digit code. But the Postal Service's response clearly did not convince the administration that the longer ZIP, intended to allow more automation and thus increase mail-handling efficiency, could do that without burdening postal customers with higher costs.

"On the basis of information provided thus far, we cannot determine whether or not your proposal comports with the regulatory principles set out in the executive order," OMB Associate Director James C. Miller told Bolger in a letter dated May 22 and released yesterday by the office of Sen. David F. Durenberger (R-Minn.), an opponent of the expanded ZIP.

In forwarding that information, Bolger apparently had sought to argue that OMB had no authority over the quasi-independent Postal Service. OMB thinks otherwise. "The language adopted in the executive order is the same as the language contained in the Paperwork Reduction Act of 1980," Miller wrote. ". . . Our general counsel has concluded that the Postal Service is indeed covered."

OMB spokesman Ed Dale yesterday referred to the letter as a request, but acknowledged that "This is a nuance of words. If we ask an agency not to do something, it is understood that they will not do it. . . . OMB, after all, does speak for the president."

A spokesman for the Postal Service said it would attempt to answer OMB's questions about its so-far zipless code within the next week or so.

But an aide to Durenberger was skeptical. The senator had tried to get the same cost-benefit information in seven months of hearings, he noted. "If they can put it together in a week, more power to them."