MOSCOW (AP) _ President Reagan said in a message to a U.S.-Soviet business group today that commerce is essential to better relations between the superpowers, and called for more non-strategic trade.

Reagan's message was read by U.S. Commerce Secretary Malcolm Baldrige at a meeting of the non-governmental U.S.-U.S.S.R. Trade and Economic Council, holding its largest-ever conference in Moscow. American officials are attending for the first time in seven years.

Baldrige later met with Soviet leader Mikhail S. Gorbachev at the Kremlin. Details of their talks were not immediately available. Baldrige was scheduled to attend a Kremlin dinner this evening.

Conference delegates, American businessmen and Soviet trade officials, said they are optimistic about U.S.-Soviet commerce following the Geneva summit between Reagan and Gorbachev.

Since 1979, the United States has dropped from the Soviet Union's second most important trading partner in the capitalist world to fifth place.

Non-agricultural trade fell from a peak of $748.7 million in 1979 to $465.8 million in 1984. Total U.S.-Soviet trade was $3.8 billion last year, including $3.2 billion in American exports, mostly farm products.

The Soviets say they want to boost trade with the West, but want to cut into their deficit by exporting more. The Soviet Union also is interested in Western technology, including computers, although Kremlin officials insist they can get along without it.

Baldrige reaffirmed U.S. Export restrictions on technology and products with military uses in a dinner speech Monday, and Reagan repeated the sentiment in his message.

''The U.S. government supports the development of non-strategic trade with the Soviet Union,'' Reagan said in the message. Reagan told the 400 U.S. delegates and their Soviet partners that their work ''is important because it brings together commercial leaders from the United States and the Soviet Union.''

''General Secretary Gorbachev and I decided in Geneva that such exchanges and contacts are an essential part of the long-term effort to build a more stable relationship between our two countries,'' Reagan said.

''I encourage you to explore possibilities for increased trade and commercial exchanges that will benefit the peoples of both countries,'' he added. ''I wish you success.''

Baldrige said Monday that the United States and Soviet Union had taken some ''modest, relatively easy, steps'' to improve their trade relationship. However, he said the most important problems are yet to be solved.

''Our trade relations cannot be viewed separately from our overall relations ... The trade relationship cannot move independently of progress in other elements of the bilateral relationship,'' he said. Soviet Foreign Trade Minister Boris I. Aristov said in a speech that the meeting was taking place ''in a special time.''

The Geneva summit, he said, ''offered a chance for a turnabout to the better in Soviet-American relations.''

''What are needed are concrete, practical steps in the spirit of the joint statement'' issued by Gorbachev and Reagan in Geneva, Aristov said.

Aristov said he and Baldrige had decided in a meeting Monday ''to continue our efforts to improve the situation in this area .. . to seek with renewed energy new possibilities to develop mutually advantageous trade.''

Dwayne O. Andreas, co-chairman of the council and head of the agriculture processing company Archer Daniels Midland Co., also referred to the summit in his speech to the meeting.

''None of us has to be told the importance of that summit ... It is the principle reason we are here today in such force, why we are finally beginning to feel a sense of confidence about the future,'' he said.

Andreas addressed Soviet concerns about U.S. trade restrictions on technology and laws allowing the government to interfere with fulfillment of existing contracts.

''It is charged that Soviet business officials are turning away from the American market because they question the reliability of U.S. companies as a supplier,'' he said. ''It is a Soviet concern that American business can understand ... We are all in this boat together and we are working for improvements.''