In the hundreds of trips she made across the U.S. Marine Corps' Quantico reservation, 72-year-old Elva Cornwell was never stopped at the military checkpoint on Fuller Road near Triangle.

That is, until last Wednesday night.

"It really shook me up. In all the years I've been driving, it was the first time I was stopped by a policeman, an MP or anything," recalled Cornwell, who lived in Triangle for more than 45 years before moving recently to Alexandria.

"I felt like a fool getting out of my car and opening the trunk with all those men standing around. They didn't have to hassle a old, gray-haired lady like that."

Protests like Cornwell's over the Corps' policy of random searches of cars on Fuller Road are nothing new in Quantico, a small community dependent on the Marines for much of its economy. In the year since the base commander ordered the inspections, there have been petitions, angry calls to politicians and at least one lawsuit over the policy.

Tomorrow, the General Assembly will get into the act. A legislative panel studying Fuller Road will hear from Quantico residents and the Marine Corps at a special hearing in the town's community hall.

"We're looking into what rights the Marine Corps has, and what rights the motorists who use the road have," said state Del. Floyd C. Bagley (D-Dumfries), a four-term legislator and former Marine captain who represents Quantico. "The Marines have criminal jurisdiction on that road, but there's no reason to go searching cars without probable cause."

Fuller Road, which crosses the 60,000-acre Marine reservation, is the only highway with access to Quantico. In 1948, a district court judge ruled that although the U.S. government technically owns it, the thoroughfare is still public.

"It's the government's road, and Lt. Gen. Carey's Richard E. Carey, Quantico's commanding officer first responsibility is to the security of this base and it's his prerogative to institute this policy to acheive that," said Maj. Jim Pendergast, Carey's spokesman.

Carey's policy of having cars searched, along with other measures, has drastically reduced drug use on the base, Pendergast added. "We don't want to cause any problems with the public, but the inspections have turned up drugs," he said.

Cars marked with military or visitor bumper stickers are subject to search at all times, since such vehicles have the run of the base. Cars using Fuller Road merely to get to and from Quantico may pass unimpeded, according to the Marine policy.

Cornwell, whose daughter and son-in-law live and work on the base (he is a Marine major), has a military sticker on her front bumper. She was driving home after dinner with them when she was ordered to the roadside and her 1980 Thunderbird was searched.

She remains angry about the incident. "I knew I had nothing to hide, but they said that every third car had to be inspected," said Cornwell, who said the Marine guards were polite, apologetic--and thorough.

She turned over her driver's license and car registration, and the Marines used flashlights to search under the floor mats, in the glove compartment and trunk.

"I told them that all they'd find in there were jumper cables, and that's all they found," she said.

Pendergast called that inspection "unfortunate" and said he will attend tomorrow's hearing, set for 10 a.m. in the Lillian W. Carden Community Center, 222 Third Ave., Quantico, to respond to any residents' complaints.