A Montgomery County junior high school has suspended the 15-year-old son of a high-ranking diplomat at the Embassy of Gabon after police and fire authorities identified the youth as their chief suspect in two fires that caused $31,000 worth of damage at the school last month.

County authorities said they were unable to arrest the youth and charge him with the counts of arson and one count of burglary because, as the son of an embassy counselor, he has diplomatic immunity from criminal prosecution.

"If it were a normal situation, he would have been arrested. It's as simple as that," said Lt. Carvel Harding, Montgomery County fire investigator.

Instead, county authorities took their information about the fires at Bethesda's Western Junior High School to Richard Gookin, the State Department's Deputy Chief of Protocol, whose office serves as an intermediary between the U.S. government and the foreign diplomatic corps here.

Gookin said yesterday that he was "very much concerned" about the case and immediately informed the embassy about the police reports.

Embassy officials could not be reached for comment yesterday. The youth and his mother both denied the charges in separate telephone conversations.

"Why would I burn the school?" the youth asked.

The youth qualifies for the diplomatic immunity from all criminal charges and most civil suits because his father holds an "A-1" visa given to diplomats and their immediate families.

About 2,000 diplomats living in the Washington area have this status.

Diplomatic immunity exempts them from everything but certain real estate contracts and civil litigation involving wills and estates. In addition, professional or commercial activities outside their official functions may be subject to lawsuits resulting from their businesses, Gookin said.

Gabon, a republic on the West African coast, was formerly under French control, and is about the size of Colorado. It has a population of $530,000.

According to Montgomery County fire authorities, the first blaze, which caused about $30,000 in damage, started in a physical education teacher's office, and spread to the girls' locker rooms and nearby areas. The fire burned itself out by the time firemen reached the scene shortly after an alarm at 8:53 a.m. on April 21.

The night before, the school and been open for a dance sponsored by the recreation department, and fire officials surmise that the blaze started sometime during the night.

Fire authorities said they identified their suspect after learning that a youth had had an argument with a physical education teacher about a tape recorder the day before the fire. The tape recorder, which had been confiscated by the teacher and locked in his office, was missing when firemen arrived at the scene of the first blaze, they said.

A few days later, the missing tape recorder was found. It was then locked up in the principal's office. Later that day, fire authorities said they were prepared to seek the end of the state department protocol office. Before they could make the official contacts, they had another fire on their hands.

This one was discovered at 2:39 a.m. April 27 when a police officer drove by the school and noticed smoke on the inside. He went in, confronted a youth in the hall, but in the confusion of the fire, the youth got away.

Fire authorities discovered six separate fires in the main school office, one of them on top of the principal's desk, one on the bulletin board and another around a clock.

A police dog called in to the school followed the suspect's trail, but lost it at an intersection in the rain, fire authorities said. The next morning, the police officer who had seen the suspect went to the diplomat's house to make a positive identification. As he was walking up the driveway, he saw the youth leaving the house and told fire authorities it was the same person he had confronted the night before.

"Apparently the parents were not cooperative at all," said Fred Cissel, another police investigator in the case. "They spoke enough English to say they had diplomatic immunity, but the rest was difficult because it was French."

It was then that police and fire authorities telephoned Gookin's office with their information. He told them that he needed written reports before he could intervene. Court officials said they have mailed those reports, but Gookin had not received them yesterday.

Meanwhile, William Snyder, principal of Western Junior High, suspended the diplomat's son last Friday after the second fire.He further recommended that the youth be expelled.