Three Prince George's County teenagers were arrested yesterday in connection with last Sunday's rock-throwing incident that injured seven people on the Capital Beltway.

Two of the suspects are 18 and the third is 17, and all three live near where the incident occurred, authorities said. The arrests were made through the joint efforts of state and Prince George's County police, officials said.

The 18-year-olds were identified as John Lavin Burgess, of Talbert Drive in Forest Heights, and Maurice Edward Ford, of Colony Road in Oxon Hill. Police said both graduated last week from Oxon Hill High School. The name of the 17-year-old was withheld because of his age.

The rock-throwing incident, which left Destiny Morris, 15, of Hagerstown, Md., in critical condition, provoked outrage from residents and officials throughout the Washington area. Police received a stream of tips, and repeatedly canvassed the area where the incident occurred.

Authorities said the arrested youths gave statements to police but they declined to characterize them.

In an interview last night, Maryland State Police Capt. Johnny L. Hughes said investigators believe the rock-throwing incident was "just a spur-of-the-moment-type thing."

"Young people do these very irresponsible things not intending to hurt someone and not realizing the seriousness of the consequences," he said.

Police said each of the two 18-year-olds was named in warrants charging them with destruction of property, a misdemeanor, and with assault with intent to murder, a felony. Authorities said the 17-year-old had not been charged as of late last night.

State Police Maj. Gary Moore said the arrests "came as the result of many interviews with people in the area of the crime" during an around-the-clock investigation in which more than 100 homes were canvassed. One police source said people interviewed Thursday provided names that led to the arrests.

Police said Ford was arrested at 3 p.m. and Burgess about five hours later. Police said the 17-year-old was picked up at the Woodstock Job Corps Center in Baltimore County.

"Even though this does not lessen the tragedy," said county police Capt. Larry Doman, of the criminal investigations unit, "we hope this will send a message."

Witnesses said three youths who appeared to be 14 to 18 years old were standing in Beltway traffic lanes near Livingston Road in Oxon Hill about 2:30 a.m. last Sunday.

The youths were throwing rocks at cars, witnesses said. At least 25 vehicles were struck, police said. The missiles were gray rocks used for landscaping, ranging in weight from five to 15 pounds.

Police said the speeds of the passing cars intensified the impact of the rocks, which hurtled into windshields and slammed into fenders, causing some motorists to momentarily lose control of their cars. "It was a real mess," a state police sergeant said.

Destiny Morris was on the way home after a Memorial Day holiday weekend in Ocean City, Md., when she was struck on the head by a rock that crashed through the window of the car in which she was riding. She remained in the intensive care unit at Southern Maryland Hospital Center last night.

Witnesses told authorities that they had seen three youths running from the scene. Police distributed fliers at apartment complexes along Livingston Road and went door to door to ask for help in solving the case. They mentioned Destiny Morris's injuries in their interviews.

Police also visited high schools around Livingston Road to enlist the aid of school officials and students.