Few events better illustrate the shift in U.S. policy toward the Soviet Union than the career of Larry Brady.

Two years ago Brady was hounded out of his sensitive Carter administration job in the Commerce Department where he was acting director and deputy director of the office of export administration. He was branded a right-wing crazy and forced into relative obscurity after telling Congress his bosses underestimated the dangers of the Soviet threat and their policies unwittingly provided the Russians with strategically potent high technology. Detente was in, so Brady was out.

But now Brady's back and he holds an even higher Commerce Department position than before, helping President Reagan decide, of all things, Soviet trade policy. And he's picked up where he left off in his criticism of the Carter administration's Soviet policy.

"The Carter people" never formulated a policy, said Brady, assistant secretary for trade administration. "Carter had a policy-level review. It never culminated in any decisions. There was a lot of ad-hocism, using foreign policy" such as Carter's decisions to halt trade in certain goods because of Soviet persecution of dissidents, its invasion of Afghanistan or human rights violations, Brady said.

"Carter had no policy. That's what bothered the allies, that's what bothered the Europeans," Brady continued.

But the strident anti-Sovietism that made Brady an outcast in one administration has made him an insider in the Reagan government. He and the president see eye-to-eye. "I wouldn't be here if that wasn't the case." Brady said he briefed Reagan on Soviet trade before the New Hampshire primary and obviously impressed the future president.

Since taking office, Brady's bunch in Commerce has wasted no time in devising tough new guidelines for exports to the Soviets and other Communist nations. Since coming to office, Reagan and his staff have rejected the notion of detente espoused by the Nixon, Ford and Carter administrations for tough talk with the Soviets.

One exception has been the lifting of the Soviet grain embargo, which Brady said did not contravene Reagan's hard line, but was unfairly hurting farmers and had outlived its usefulness.

Also, Reagan this month authorized the sale to the Russians of 100 pipe-laying machines made by Caterpillar Tractor Co. President Carter had imposed stringent export controls on American goods that might have strategic applications. The machines, however, will not be used on the controversial natural gas pipeline project linking Russia to West Germany and France, which the Reagan administration has opposed, Brady said.

Brady defended the Caterpillar decision saying the Soviet Union would be able to buy the pipe layers from other countries, and they would not be used on the pipeline. When asked how the U.S. government can prevent the Russians from using the machines on the pipeline, Brady conceded that it can't.

"We cannot control whether Soviets take those pipe layers and use them on the" pipeline. But if they did, "it would affect our willingness and the disposition of future cases," Brady said. "This does not change the administration's position on the pipeline. That's a separate matter."

Brady said the Henry Kissinger-approach to detente -- assuming Soviet behavior can be controlled by trading with them -- hasn't worked. Brady quickly ticked off actions by Carter that he said never would be accepted by Reagan.

For example, Brady said Reagan never would have allowed American air traffic controllers to help the Soviets with their system. The Americans were helping the Russians track foreign and domestic aircraft, Brady said.

Reagan also never would have allowed export of technology that permits Russian detection of U.S. submarines or sale of know-how to help the Russians build the heavy vehicles, which were subsequently used in the invasion of Afghanistan. "The trucks were made with Western and U.S. know-how," Brady said. "The Soviets couldn't make an engine block that wouldn't crack."

A big worry in the 1980s will be to relieve growing pressure on the Western Europeans to trade with and ultimately become dependent on the Soviets, Brady said. "That's the real concern with the pipeline, the real dependence on the Soviet market by Western Europe."

"The thing we have to look at is vulnerability," Brady said. "We've got to be very, very cautious, and I think that's the position of this administration."

Rather than concentrate on individual products, Brady said the new trade policy toward the Soviets will stress restricting the transfer of technological know-how. "But that doesn't mean we won't have product control," Brady said.

However, the policy doesn't address trade with Communist Asian countries, but only the Soviet Union and its satellites and the Peoples Republic of China. Brady defended the governnment's decision to allow the Chinese to buy strategic equipment. He said the Chinese, unlike the Soviets, aren't determined to dominate the world and they "have a long, long way to go" before they are a real military threat.