In what one State Department official called the "fastest agreement ever reached on anything between the two governments," the United States and the Soviet Union have arranged in trade a parcel of lush, wooded land on Maryland's Eastern Shore for two pieces of property in Moscow.

The Russians will get four acres on Pioneer Point in Queen Anne's County as a summer retreat. The property adjoins a 45-acre tract they already own. In exchange, the State Department received two Moscow parcels, where it will build recreational facilities and a warehouse.

The State Department has agreed to pay $400,000 for the Eastern Shore property, which it will then lease rent-free for 85 years to the Russians. In return, the State Department will get similar leases on the Moscow land.

The Russians had been asking about $2.5 million in rent for far shorter-term leases on the Moscow properties, and by those terms, "we got a great bargain," department official Charles Swan said yesterday.

The exchange was first suggested early this year by Soviet Ambassador Anatoliy Dobrynin, according to Swan. Then in May New York's Chase Manhattan Bank, which owns the Maryland property, suddenly put on the pressure with news that it had another interest buyer. The soviet-American deal was struck 10 days later after a flurry of diplomatic cables and delicate negotiations, Swan said.

"Probably during World War II, some things went through faster, but in recent memory this is the fastest the two countries ever worked out an agreement," he said.

The exchange may even have helped ease the way to a long-delayed construction contract between the two countries, allowing the United States to begin building a new embassy complex in Moscow. After seven years of negotiations, the contract was signed June 30.

"I can't tell you what their motives were" for reaching final agreement on that, Swan said, but the land exchange, "sure didn't hurt anything."

The Pioneer Point property involved in the exchange once belonged to millionaire John Jacob Raskob, builder of the Empire State Building. The 45-acre tract the Russians already oww contains Raskob's two neo-Georgian mansions, and the new four-acre parcel contains a stately white home, one used as servants' quarters and since renovated as an office building.

Joe Handley, the 80-year-old estate manager who once worked for Raskob and still oversees the remainder of the 1,600-acre estate, said Dobrynin and his wife visited the site last spring.

The ambassador carefully inspected the building and said he planned to build tennis courts and a swimming pool on the grounds, Handley said.

Officials at the Soviet embassy in Washington were unavailable for comment yesterday.

Handley, one of the loudest protesters when the Russians first arrived at Pioneer Point in 1972, has changed his mind.

"As far as neighbors are concerned you couldn't ask for better," Handley said yesterday."They don't bother anybody. CAPTION: Picture, Stately white home that has been renovated as an office building is on the four-acre tract leased to Soviet embassy as part of trade for Moscow property. By T. Gregory Lynch for The Washington Post; Map, no caption, By Richard Furno - The Washington Post