Hours after the superpowers resolved anti-cheating issues blocking Senate debate on ratifying a nuclear missile-ban treaty, another hitch emerged, U.S. officials said Friday.

The new dispute kept American and Soviet negotiators up through the night before it was settled shortly after dawn.The disagreement was over the size of canisters that could leave a Soviet missile assembly plant without being subject to U.S. inspection.

"They are hard bargainers," Secretary of State George P. Shultz told a news conference at NATO headquarters. "They keep trying us on for size."

He did not accuse the Soviets of bad faith but said the United States would remain on guard as the treaty to scrap intermediate-range missiles is implemented.

In Geneva on Thursday, Shultz wound up negotiations with Soviet Foreign Minister Eduard A. Schevardnadze and declared: "We feel all of the issues have been dealt with satisfactorily."

But a few hours later, the Soviets telephoned U.S. negotiator Maynard Glitman to demand a revision.

The argument raged through the night in Geneva and was settled with agreement that all canisters longer than 46.2 feet must be subject to inspection. The Soviets had wanted the figure to be 67.7 feet, a U.S. official said.

The official, speaking on condition of anonymity, said the United States wanted to make sure parts for missiles banned by the treaty were not illegally shipped from the plant.

He said, however, such a Soviet violation was extremely unlikely.

The dispute was disclosed to reporters as Shultz flew to Brussels to brief North Atlantic Treaty Organization foreign ministers and other allied officials on the negotiations in Geneva.

After being briefed by Shultz, the ministers said they were pleased that the last-minute hitches had been resolved.

"We very much welcome what Secretary Shultz had to say today," David Mellor, a British minister of state, told reporters.

Hans-Dietrich Genscher, the West German foreign minister, said it was important that the treaty banning medium-range nuclear missiles be ratified by the U.S. Senate and implemented as soon as possible.

Genscher, in remarks to reporters, said the treaty was "a significant contribution to the unity, firmness and cohesion of the Western alliance."