Four people were killed yesterday when two single-engine planes crashed and burned -- one in the Virginia hunt country after taking off from Dulles International Airport, the other in the back yard of a house in Greenbelt as it apparently headed toward a suburban Maryland air field.

Both crashes, which occurred about 60 miles apart within 2 1/2 hours, were under investigation. No one on the ground was injured.

The Northern Virginia crash occurred about 3:30 p.m., and the two men aboard were burned beyond recognition. Documents found inside the airplane indicated that they were an Arkansas chiropractor and a Kansas lawyer who authorities said had participated yesterday morning in a briefing on the Clinton administration's health care plan.

A man and a woman, both Prince George's County residents, were killed in the Greenbelt crash, which occurred a few minutes before 6 p.m. They had taken off from Hyde Field in southern Prince George's.

Those killed in the first crash, near a country road in Fauquier County, were identified as chiropractor Stanley Heard, of Hot Springs, Ark., and Steven Dickson, of Topeka, Kan. The site where the six-seat Piper Cherokee crashed is just north of Marshall, Va., about 50 miles west of Washington.

Dickson apparently was flying the plane. His law partner, Judy Pope, said last night that Dickson flew his own plane from Topeka, but on the way to Washington it developed problems and he landed in St. Louis. There, he left his plane for repair and rented another plane, Pope said.

Trouble aboard was reported minutes after the plane left Dulles yesterday. Margaret B. Napolitan, of the National Transportation Safety Board, who was at the crash scene, said the plane radioed to Dulles that there was a fire.

Air-traffic controllers arranged for the plane to land on an airstrip at Rokeby, a 4,000-acre cattle and horse farm owned by philanthropist and horse breeder Paul Mellon.

The 5,500-foot blacktop strip has emergency equipment and is one of several private air fields among the estates of Virginia's horse country, where some of the nation's wealthiest families have estates.

Witnesses told Virginia State Police that one of the plane's wings struck a tree about six miles south of Rokeby and 18 miles west of Dulles, causing it to bounce across a field about three times before it hit a utility pole at Route 710 and exploded.

"When he hit the tree top, that set him down," Fauquier County Sheriff Joe Higgs said. "He went boom, boom, boom, then blam, then his fuel tank exploded."

When the plane hit the pole, it knocked down power and telephone lines to about 500 residents throughout the rolling hills of Fauquier County.

The plane that crashed in Greenbelt, about 5:50 p.m., struck behind the house of Josephine Blair on Lakeside Drive.

The pilot was identified as Roger Pasteur West, 41, of the 10000 block of Locust Street, Glen Dale. His passenger was Valerie Neill Maddox, 42, of the 9500 block of Oakleaf Place in Clinton, police said.

The plane, a two-seat Cessna 150, had taken off from Potomac Airport in Friendly on what was described as a "local flight," said Jeff Guzzetti, an investigator with the National Transportation Safety Board.

Pete Piringer, spokesman for the Prince George's County Fire Department, said it appeared that the plane had plummeted into the ground almost vertically, suggesting that it may have stalled.

Piringer said he thought it possible that the pilot was "looking for the College Park airport" when the plane crashed.

Neighbors said they had seen the airplane circling at a low altitude for as long as 20 minutes while its engine sputtered and sounded as if it was stopping and starting.

Some neighbors said it appeared to them that the pilot swerved the plane as it came down to avoid a nearby recreation area where dozens of youngsters were playing football. "The angle that he was heading in looked like he was going to crash right into the football field," said Jim Ittenbach, who had dropped his 8-year-old son there for football practice. "Then he cocked the wing, swerved away from the field and the plane went straight down. I think it was intentional."

The plane landed about 10 feet from a two-story brick rambler in the unit block of Lakeside Drive.

A neighbor, Bruno Zanin, said flames from the wreckage leaped about 25 feet. The plane "was just a ball of flame," he said.

Piringer said a volunteer firefighter who lives nearby used a garden hose to keep the flames in check. The firefighter and another neighbor wanted to rescue the plane's occupants, but there was "really nothing they could do," Piringer said.

Dickson, the lawyer who apparently was piloting the plane that crashed in Northern Virginia, was active in the Democratic Party in Kansas. He ran unsuccessfully for Congress in 1984.

Dickson, a bachelor, specialized in aspects of law concerning chiropractic. He was special counsel to the National Chiropractors Health Care Advisory Committee to the Clinton administration. Pope, his law partner, said that is how he met Heard.

Heard was also active in Democratic politics, and Clinton had appointed him to an Arkansas chiropractors' ethics committee when Clinton was governor of the state, according to John E. Nelson, a retired chiropractor in Hot Springs.

Heard's twin boys, Dexter Heard and Dustin Heard, were involved in a lawsuit in 1984 in which Heard and his wife, Penney, sued the local school district for suspending their children from school because they had not been immunized. The Heards lost the case, which went to the Arkansas Supreme Court.

West, the pilot of the plane that crashed in Greenbelt, was an engineer with C&P Telephone Co. in the District and had lived much of his life in Prince George's County, according to a relative. West, an Air Force veteran, loved flying, the relative said.

Maddox was an engineering assistant who grew up in Forest Heights, according to people reached by phone at her home.

Staff writer Stephen C. Fehr contributed to this report.