May 31, 1986

The material that Ronald W. Pelton is charged with providing to the Soviet Union offers a detailed account of this country's successes, and failures, in intercepting many of the communications networks in the Soviet Union, a senior official of the National Security Agency testified today. The official, William Perry Crowell Jr., said the data would be of great value to Soviet agents because it would allow them to ''render ineffective'' some of the costly devices used by American intelligence to eavesdrop on Soviet communications. He said the data could also be used by the Soviet Union to ''capitalize on our weaknesses'' since it describes which signals the N.S.A. has failed to decode or intercept. Mr. Crowell, identified as the chief of the N.S.A. group that collects and analyzes Soviet communications, provided the most detailed account to date of the damage that may have been caused by Mr. Pelton's activities. Among these were disclosures about Project A, an interception program that had provided American intelligence with a ''considerable amount'' of information on training, capabilities and planned maneuvers of unspecified Soviet military forces.

Secretary of State George P. Shultz said today that the United States, in a policy ''shift of gears,'' would decide what nuclear weapons were needed for its security on military grounds and no longer on ''the technicalities'' of the 1979 arms treaty with the Soviet Union. In a news conference at the end of a turbulent two-day meeting here of the NATO foreign ministers, Mr. Shultz said he did not want to ''underestimate'' the value that might accrue from achieving ''radical reductions'' in nuclear arms through a future arms accord with the Russians. But with the chances of such an accord admittedly slim, Mr. Shultz seemed in his comments to be seeking to justify to the American and allied publics President Reagan's announced shift away from dependence on the 1979 treaty to help maintain strategic parity with the Russians. That accord, which was never ratified by the Senate, set limits on the numbers of offensive long-range missiles and bombers in the Soviet and American arsenals.

The vice chairman of the United States Postal Service's Board of Governors pleaded guilty today to taking illegal payoffs in exchange for trying to steer a $250 million postal contract to a Dallas company. The executive, Peter Voss, also pleaded guilty in Federal District Court to embezzling money from the Postal Service. Prosecutors said he was reimbursed for first-class airline tickets when he actually traveled in coach class. He Resigns From Board Mr. Voss immediately resigned from the eight-member board, which is expected to award the $250 million postal contract later this year.

More than a month after the Unit 4 reactor at the Chernobyl atomic power station erupted with a plume of radioactive dust, Kiev and its 2.5 million people are learning to live with the invisible threat that stirs with strong south winds - the ''dust,'' as people call it. The shadow of Chernobyl is not immediately evident in the bright sunshine of a spring that people say is the best in many a year. But reminders of the dust are never far away. The hand-printed sign at the back of the ornate Bessarabsky farmers' market directs sellers to the dairy section around the side.

A former clerk in a stock brokerage has been charged with putting rat poison in capsules of Contac cold medicine and two other drugs in an attempt to profit through stock trading. Federal agents arrested the former clerk, Edward Arlen Marks, an unemployed 24-year-old and a former convict, on Thursday night, and he was arraigned today. The F.B.I. said its agents were led to Mr. Marks by a fingerprint found on a poisoned capsule package, which matched a print in its files. Unusual Trades Drew Notice The case began March 20, after a caller told news organizations that packages of the three drugs, all made by the SmithKline Beckman Corporation, had been tampered with. Today the bureau said that at about that time Mr. Marks had purchased several hundred options to sell stock. The options would gain sharply in value if SmithKline stock plunged. In fact, SmithKline stock declined only slightly at the time, and the F.B.I. said Mr. Marks did not profit on the options. But the unusual trading at the time of the tampering drew notice, the bureau said.