Norwegian police have uncovered a 10-year pattern of illegal sales of high-technology equipment to the Soviet Union by companies based in France, Italy and West Germany for use in improving the Soviet navy and in building nuclear weapons, Reagan administration and congressional sources reported yesterday.

The diversions were discovered by Norwegian authorities as part of an investigation into illegal sales by Kongsberg Vaapenfabrikk, a state-owned arms company. The investigation was triggered by the discovery that Kongsberg and Toshiba Corp. of Japan had sold computerized milling machinery to the Soviets.

The Toshiba sale, according to the Pentagon, allowed the Soviets to develop quiet submarine propellers that can evade U.S. surveillance.

The sales violated the laws of the countries in which the individual companies are based.

The report of the Norwegian investigation, which will be released today in Oslo and Washington, also found that a British firm may have illegally sold high-technology milling machines to China.

In all, more than 60 computer-controlled, multiaxis milling machines were sold to the Soviets from the mid-1970s until just a few years ago, sources said. Most of that equipment went to Soviet shipyards.

But a senior administration official, citing other intelligence information, said he believes a West German firm, Schiess Aktiengesellschaft, sold the Soviets 21 milling machines that may have ended up in a Soviet nuclear weapons facility. "They are very sophisticated machines with high tolerances" of the type needed to manufacture nuclear weapons, he added.

In all the sales, Kongsberg supplied the controllers, described by one source as "the brains of the operations," for multiaxis, sophisticated milling machines manufactured and sold by the other Western companies.

"The dimensions are enormous. The Toshiba violation itself could pale against what else has gone one," said a senior administration specialist in export controls.

"It shows a systematic effort by Kongsberg over 10 years to outfit multiaxis milling machines {with the needed controls} for sale to the communist bloc. We've got a pattern in which the Soviets have successfully and easily brought this equipment into their country," he added.

He suggested that it shows the Paris-based Coordinating Committee for Multilateral Export Controls -- known as COCOM and composed of Japan and the NATO allies of the U.S. and Iceland -- may be "a hollow shell."

The Norwegian investigation also turned up information that U.S. companies may have supplied sophisticated computers to the Soviet in violation of COCOM rules. This information has been turned over to U.S. agencies for investigation, the source said.

Most of the attention in this country has been focused on the sale of computer-controlled milling machines by Toshiba, with the Senate overwhelmingly approving a provision in the trade bill that would punish the Japanese electronics giant by banning sales of all its products in the United States for as long as five years.

But the Reagan administration, especially the Defense Department and the National Security Council, has tried to use the sales to demonstrate how diversions undermine the entire Western security net. They want to force Japan and Norway to institute massive improvements in their export control laws and enforcement procedures.

As a result of the findings of the Norwegian investigation, administration officials now say that the other COCOM members must follow the example set over the past four months by Japan and Norway. Senior export control experts from the Commerce, Defense and State departments are fanning out through Europe this week to pressure COCOM members to upgrade their participation in the organization and tighten their laws against the diversion of technology to the Soviet bloc.

The Norwegian finding is also likely to take some of the political heat off Toshiba and other Japanese companies that have borne the brunt of congressional pressure in this area.

Yesterday, for example, Republican and Democratic staff members of the Senate Foreign Relations Committee called a ranking French diplomat to Capitol Hill to complain about the way that country had reported the export control violations as "minor and isolated."

To underscore that view, Sen. Jesse Helms (R-N.C.), ranking minority member of the committee, released a letter he sent to French Ambassador Emmanuel de Margerie complaining about the French attitute that its export control laws do not need to be tightened.

Helms said the French response "reflects a fundamental misunderstanding of the impact which these sales had as well as an unfortunate misjudgment with regard to the resolve of the United States to make COCOM work."

The French company -- Ratier-Forest S.A. -- was named as one of the violators in the Norwegian investigation. Reportedly, they had "multiple violations", an administration source said.

Toshiba, in its own investigation, had fingered that firm in August, reporting Ratier-Forest had sold similar machines to the Soviets before it did. The French said their machines involved a lesser degree of technology than those supplied by Toshiba.

Administration and Hill sources said the other companies named in the Norwegian report are Innocenti SPA, an Italian company that sold 23 machines; Schiess, the West German company that sold 32 machines; and O. Doerries GMPH, another West German company that sold five machines.