After an interruption of more than four years, the Soviet airline Aeroflot resumed flights to the United States yesterday, initiating what both U.S. and Soviet officials called a new era in communicaton between their nations.

About 70 Soviet officials and journalists, looking rumpled in three-piece suits after an 11-hour inaugural journey, touched down at Dulles International Airport at the scheduled arrival time of 2:30 p.m. yesterday. A few hours earlier, a Pan American Airways flight had become the first commercial American airliner to land in Moscow since 1978.

"The Soviets are ready to continue the progress that was started in Geneva," said Michail Timofeev, Soviet deputy minister for civil aviation, at a Dulles news conference after the arrival. "The route across the ocean is a safe one and a practical one."

President Reagan and Soviet leader Mikhail S. Gorbachev decided last fall in Geneva to renew commercial air service to help carry out cultural, scientific and educational exchanges between their countries, ending four years of negotiations over commercial airline service.

"This is a particularly pleasant and a potentially very fruitful occasion," Richard Mathias, Pan Am's senior vice president for government affairs, said in a joint appearance with Soviet officials at Dulles.

President Reagan terminated Aeroflot service to the United States in December 1981 in reaction to the Soviet imposition of martial law in Poland.

Pan American airlines suspended its service to the Soviet Union in 1978, saying the flights had become uneconomical.

Since then travelers have had to fly to European cities from the Soviet Union or United States to make airline connections between the two countries.

Under the terms of the new agreement, each airline will schedule four round-trip flights each week. Aeroflot will fly twice a week from Moscow to New York and Washington. The Soviets will use the Ilyushin Il62, the workhorse of the Aeroflot fleet.

Pan Am will schedule four flights each week from New York to Frankfurt, where passengers will change planes for the final leg to Leningrad on Pan American.

Aeroflot, the world's largest commercial airline with almost 500,000 employes, has flown more than 500 million passengers in the last five years.

Pan Am and Aeroflot will share some of the profits from the service between the United States and the Soviet Union, according to Pan Am spokesman Merle Richman.

In the past, Aeroflot held an edge in the market, with virtually all Soviet travelers to the United States using the airline, and many Americans flying Aeroflot for the experience, a Pan Am official said.

Mathias said yesterday that many of the Pan Am flights during the busy summer months are already fully booked. The lowest individual round-trip fare between the two countries will be about $1,000. Prices for Aeroflot tickets were not available yesterday.

Pan Am officials said they hope that group tours and more official visits will help it turn a profit. During the peak of its service, almost 100,000 Americans traveled to the Soviet Union each year.

"I would definitely go there," said William O'Brien, who watched the festivities yesterday at Dulles as he waited for the continuation of his flight from Tampa to Boston.