Dynalectron Corp. of McLean disclosed yesterday that it has signed a multimillion-dollar agreement with Germany's largest coal producer to aid development of Dynalectron's process for making synthetic fuel from coal.

Dynalectron said Ruhrkohle, A.G. has agreed to pay $1 million for a one-year option to buy European rights to Dynalectron's process called H-coal.

Ruhrkohle and the German state of North Rhine-Westfalia, also agreed to invest $5 million in the H-coal synthetic fuels pilot plant at Cattletsburg, Ky., which is scheduled to begin turning coal into oil next month.

If the West German firm decides to buy continential rights to the process, it will pay Dynalectron an additional $6.5 million plus a license fee for every H-coal plant built.

Dynalectron also could collect millions more for designing and engineering H-coal plants in Europe, company officials said.

The agreement with the German firm gives it rights to build H-coal plants in the Soviet Union. For the time being, however, any dealings with the Soviets would be prohibited by President Carter's ban on export of high technology to Russia.

Dynalectron President Charles Gulledge said the agreement with the Germans should help commerical development of the H-coal process both in Europe and in the United States.

Ruhrkohle is already going its own research on other ways to make liquid fuels from coal, Gulledge noted. "To have them select our process as the one they wish to be associated with is very significant," he added.

Ruhrkohle, A.G., is the largest coal producing company in West Germany; like most German industrial corporations it has ties to the government of the Federal Republic.

In addition to its investment in Dynalectron's synfuels process, Rohrkohle also is involved in research using the synthetinc gasoline process developed by the Germans during World War II.

The H-coal process was developed by Hydrocarbon Research Inc., a Dynalectron subsidiary with laboratories in Trenton, N.J.

The HRI system was originally devised to remove impurities from heavy crude oil and to upgrade tarlike oils to make them usable as fuels. The Cattleburg, Ky. pilot plant began running on oil last month and after a couple oc months of shakedown runs will begin making oil from coal.

The plant is designed to turn 600 tons of coal a day into 2200 barrels of "syncrude" or man-made crude oil. When oil conversion operations begin -- probably in late April -- the Cattlettsburg plant will be the largest synthetic fuels factory in America.

Ruhrkohle's $5 million will provide additional capital for the H-coal pilot plant, which is a joint venture of the U.S. Department of Energy, the commonwealth of Kentucky, the Electric Power Research Institute; and affiliates of three big oil companies, Mobil, Ashland and Conco.

The Kentucky plant is supposed to provide the engineering know-how and operating experience to permit construction of a commercial scale plant capable of producing 50,000 barrels of synthetic crude a day.