Transportation Secretary Elizabeth Hanford Dole announced yesterday a tentative agreement to resume direct commercial airline service between the United States and the Soviet Union.

Pan American World Airways, which will be the U.S. airline, said the service could begin as early as April 27. Aeroflot will be the Soviet carrier.

The agreement, which must be reviewed by both governments before final approval, came the day after the conclusion of the Geneva summit conference between President Reagan and Soviet leader Mikhail Gorbachev.

One of the agreements announced at the summit -- a pact to improve the security of civil airliners flying the busy North Pacific routes from Anchorage to Tokyo -- was considered by the United States to be a precondition for resumption of Soviet-U.S. commercial air service.

The Soviets have wanted to resume Aeroflot service to the United States since Reagan terminated it in 1981 in reaction to Soviet actions in Poland. Pan Am withdrew from Moscow in 1978 for economic reasons, including the fact that Soviet regulations in essence barred the U.S. carrier from selling tickets.

"President Reagan said he hoped his summit with General Secretary Gorbachev would help bring the people of our nations together," Dole said yesterday. "This agreement is an immediate step in that direction."

Merle Richman, a Pan Am spokesman, said, "We're confident that, under the new agreement, we can operate the system in an economic manner."

Pan Am will be authorized to serve Moscow and Leningrad from the United States; Aeroflot will be authorized to service New York and Washington. An intermediate point will be permitted for each airline.

Pan Am's service will be through Frankfurt, West Germany, where the airline has its European hub. Jumbo-jet flights from Washington, New York, Miami, Los Angeles, San Francisco and Chicago will connect at Frankfurt with smaller-plane service to Moscow on Mondays and Saturdays and to Moscow and Leningrad on Thursdays and Fridays.

The North Pacific security agreement comes after the Soviets shot down an off-course Korean Air Lines jumbo jet over their waters in 1983, killing all 269 people on board.

Under the security agreement, a continual direct voice communications link will be established with the three international air traffic control centers covering the North Pacific -- Anchorage, Tokyo and Khabarovsk.

In addition, civil aircraft will be allowed to land in Soviet territory in emergency situations. Donald R. Segner, an associate administrator of the Federal Aviation Administration who headed the U.S. negotiating team in six months of talks, said, "This is a big step. It's the first time the Soviets have permitted anything like that."