U.S. Changes Its Stance On Damage by Toshiba

For the second time in a month, the Reagan Administration has sharply reversed its assessment of how much United States security was damaged by the Toshiba Machine Corporation's sale of advanced submarine technology to the Soviet Union.

The Administration has insisted for nearly a year after the first disclosures of the sale that the Toshiba diversion would cost Western allies billions of dollars to regain their ability to track Soviet nuclear and attack submarines, which were made quieter by the Japanese equipment. 'Difficult to Assess'

But last month, trying to head off harsh Congressional sanctions against Toshiba that would likely worsen the strains between the United States and Japan, the Defense Department seemed to quietly change the assessment.

Richard L. Armitage, the Assistant Secretary of Defense for international security affairs, said in a letter to Congressional leaders that ''the Soviets had quiet propellers three years before the first diversion,'' and that ''the actual damage done from the Toshiba Machinery diversions is difficult to assess.''

Some military and intelligence officials familiar with the case were shocked by the changed assessment when Mr. Armitage's letter became public last week. The Defense Department issued a statement over the weekend reverting to its original position that ''the Toshiba Machine diversion provided the U.S.S.R. with substantial production capability'' to manufacture super-quiet, hard-to-track submarines.

Mr. Armitage did not return telephone calls on Friday to discuss his letter.

The Administration's successive reversals were prompted by the current debate in a House-Senate conference committee over whether further action should be taken against Toshiba Machine or its parent company, the Toshiba Corporation, which owns 51 percent of the unit that sold the giant propeller milling machines to the Soviet Union.

The rapid changes in the Administration's position, military and intelligence officials say, vividly illustrates how quickly politics can alter the seemingly objective measures of technological gains and losses against the Soviet Union. Charges of Other Diversions

In this case, the Administration appears to be trying to tone down some of its rhetoric about the potential damage, while conservatives on Capitol Hill argue that sanctions should be stiff because Toshiba may have been involved in other diversions. So far, the evidence for those additional violations appears scanty at best, investigators say.

''In my view, the Toshiba case was the single worst case of technology diversion that has ever occurred because of its impact on Western defense,'' said Stephen D. Bryen, who heads the Pentagon's export control office and led the Toshiba investigation last year. ''But since then, diversions from Japan have stopped ice cold, and the Japanese are cooperating fully.''

The Administration's effort now, Mr. Bryen said, is to ''let the Japanese take care of its own and to treat Japan like a first-class nation, not a vassal state'' that is subject to punishment by the United States.

A proposal by the House of Representatives would give President Reagan discretion over whether to invoke sanctions against Toshiba Machine, which - along with Kongsberg Vaapenfabrikk, Norway's state-owned military contractor, also implicated in the transaction - is already barred from receiving Defense Department contracts. The Senate version, though, would require the President to ban all imports from the Toshiba Corporation, except for parts and components essential to American companies. 'Punishing the Guilty'

Mr. Armitage's letter, sent to Representative Les Aspin, the Wisconsin Democrat who is the chairman of the House Armed Services Committee, contended that Japan had ''succeeding in punishing the guilty, establishing stronger controls, and funding antisubmarine warfare programs which will help both the U.S. and Japanese Navies.'' Any further action against Toshiba, he said, ''would be interpreted in Japan as motivated by trade imbalances, rather than by national security concerns.''

Where Mr. Armitage departed from the Administration's earlier view, however, was in his assessment that the Soviet Union ''had quiet propellers three years before the first diversion'' in 1983. That would seem to suggest - as a group of Soviet scientists said last month at a meeting of the American Association for the Advancement of Science - that the Soviet effort was not really aided by the Japanese equipment.

Mr. Armitage's view ran counter to the conclusions of a report issued last year by the Central Intelligence Agency that stated that the Soviet Union gained the knowledge to design the quiet propellers between 1979 and 1982. But they only had the equipment to ''build a small number of experimental, prototype seven-bladed, skewed propellers,'' the report said.

In fact, the Soviet Union was probably producing a small number of quiet propellers for its submarine fleet using less-capable milling machines obtained from Forest Line, the Paris-based machinery company, in a transaction that became known after the Toshiba disclosures. But not until the first of four Toshiba MBP-110 milling machines was installed at the Baltic Shipyard in Leningrad could the Soviet Navy ''begin to automate the process,'' Mr. Bryen said in an interview last week. ''At that point, they stepped up their production from a handful to regular, full-scale production.'' Pentagon Statement

In its statement, the Pentagon made no specific reference to Mr. Armitage's letter. But the statement on how the Toshiba equipment aided the Soviet Union appears to counter Mr. Armitage's assertions.

The statement also responded to charges, made primarily by the staff members of Senator Jesse Helms, Republican of North Carolina, and Representative Duncan L. Hunter, a California Republican, that the Toshiba Corporation was involved in additional diversions to the Soviet Union. The allegations ''are not supported sufficiently by the evidence,'' the Pentagon statement said.

The charges centered on negotiations to sell a printed circuit-board manufacturing plant to East Germany, which Toshiba terminated last year after American officials intervened, and semiconductor fabrication plants that may have been sold to Czechoslovakia in 1979 and to East Germany in 1986.