Reagan administration officials are taking a low-key approach while business officials appear more optimistic heading into next week's meeting in Moscow with leading Soviet trade and government officials.

Nothing dramatic is expected from the meeting Tuesday through Thursday of the U.S.-Soviet Commercial Commission, a senior U.S. aide said.Nevertheless, 500 to 550 U.S. business officials - nearly twice the group that went to the last meeting two years ago - are expected to board a special Boeing 747 charter jet Sunday for the flight to Moscow.

This new dialogue (between Soviets and Americans) is gaining momentum, said James H. Giffen, president of the U.S.-U.S.S.R. Trade and Economic Council, which is organizing the non-government U.S. delegation at the meetings. We're starting to talk about real deals.

Some of that optimism stems from Soviet leader Mikhail Gorbachev's proposed economic reforms. More is provided by the presence of Mr. Verity, who took office last October and is more open than his predecessor, Malcolm Baldrige, to the idea of trading with the Soviets.

Last year, U.S. exports to the Soviet Union reached nearly $1.5 billion, up more than $200 million from 1986, and are expected to rise further this year. Imports from the Soviet Union last year fell about 20 percent to $470 million.

The $1 billion U.S. trade surplus with the Soviet Union was among the largest surpluses the United States had last year with any country.

Government officials said Mr. Verity, who is co-chairman of the U.S.-Soviet economic commission, will propose to the Soviets that the two sides form working groups to pursue trade in five sectors: energy, construction equipment, food processing, medical goods and services.

All are sectors where U.S. officials believe U.S. firms would be especially competitive in the Soviet market.

The decision to propose forming the five sector groups was a routine, interagency action, a U.S. official said. It did not, he said, involve Cabinet-level consultation.

Besides proposing the five groups, Mr. Verity is expected to try to clear away some of the bureaucratic red tape that has accompanied the Soviet Union's recent economic reforms. Simpler Soviet procedures might help foster U.S. sales, officials believe.

The first commission meeting since December 1986 also will contain some welcome news to Soviet ears: that the omnibus trade bill now being debated by Congress carries a provision to finally end a decades-long ban on Soviet mink, fox and other furs.

Soviet plans for joint ventures with U.S. and other western firms are likely to be explored, an official said.

Several U.S. companies, for example, hope to profit from joint ventures in energy. The Soviet Union can't take full advantage of its oil and gas reserves, the largest of any nation, because of a lack of technology, capital and managerial know-how, industry observers said.

Chevron Corp. of San Francisco said it is discussing cooperation in all aspects of the Soviet oil industry, from exploration to refining and petrochemicals.

Chevron recently sent a 10-person team to conduct geologic work in the Soviet Union, a Chevron spokesman said.

Chevron's discussions with the Soviets are still in the preliminary and exploratory stage, the spokesman said. The Soviets have reported arrangements for specific large-scale petrochemical projects that Chevron declined to confirm.

Combustion Engineering Inc., Stamford, Conn., last November became the first U.S. company to be granted an equity share in a Soviet-based joint venture.

The venture, called Applied Engineering Systems, will be 51 percent-owned by the Soviets and 49 percent by Combustion Engineering. Operations are expected to begin in January 1989. The venture's first assignment will be to upgrade a petrochemical complex near Moscow. Combustion Engineering estimates that the new venture will have gross sales of $200 million over five years. The company's initial investment is about $8 million worth of goods and services.