At noontime April 5, as scientists worried about a possible core melt-down at the Three Mile Island nuclear power plant, a group of state and federal officials huddled in a hotel room 65 miles away. On the back of a lunch menu, they charted out an evacuation plan for the city of Hagerstown, Md.

The crisis in Hagerstown had nothing to do with nuclear power. But to the select few who knew about it, the situation in the Western Maryland city was quite worrisome.

For several days, two trucks containing nearly 33,000 pounds of deadly, contaminated phosphorus sat parked near the Hagerstown airport, undergoing uncontrollable chemical reactions that caused officials to describe the material as a "ticking time bomb."

As they desperately sought a site to store or safely explode the phosphorus, they also mapped the evacuation of the valley city of Hagerstown. With urgent appeals by Gov. Harry Hughes and White House intervention, an army reservation south of Washington was finally secured as a disposal site.

Then began, in the quiet morning hours of April 16, an unusual 22-vehicle convoy bound 162 miles from Hagerstown to Fort A.P. Hill, Va.

As the caravan, its contents well-kept secret, began the trip that would take it around Washington on the Capital Beltway, the lead driver remarked over his CB radio, "Hey Harry, looks like we got us a convoy."

"It's not a convoy," his colleague replied. "It's a funeral procession."

The procession ended after 3 1/2 hours, at the Army site south of Washington. There, over the next two weeks, drums of phosphorus were systematically ignited in an unpopulated range -- a final, dramatic chapter that sent starbursts over a 1.3 mile area.

Transportation of hazardous substances has become a subject of serious and growing concern to lawmakers and citizen groups, who have lobbied for more stringent regulations to protect highway communities. No laws at present prevent the shipment of such materials, leaving open the possibility, however slim, of a disaster.

The drama began in the early morning of March 22 when a truck trailer owner by Ryder Truck Lines caught fire in Gettysburg, Pa. The trailer held 89 drums of white phosphorus, each containing 410 pounds of the substance. It was being shipped from Mobil Chemicals' Electrophos subsidiary in Pierce, Fla., to a buyer in West Chester, Pa.

Phosphorus is often used in highway flares and in fertilizer.

The accident near the center of Gettysburg scorched a Civil War monument and injured 80 people, including seven firemen and the truck driver. As the truck was unloaded the next day, it exploded again, injuring several more people.

The 30-gallon drums had been hermetically sealed to exclude oxygen that could ignite the chemical. The Gettysburg fire, however, had charred and damaged the seals. To prevent an explosion, the drums were placed in large 55-gallon containers and then covered with water.

The repackaging of the phosphorus was carried out from March 26 to 28. The use of the larger drums required two trucks to haul the same 38,000 pounds.

Headed back to Florida, the phosphorus-hauling trucks detoured to the Ryder Truck terminal just north of Hagerstown when one driver "became aware that the barrels were distended," according to Thomas Jorling, then an assistant administrator at the U.S. Environmental Protection Agency.

The trucks then sat at the terminal for almost a week while officials of Ryder and Mobil Chemical argued over who was responsible for the contents -- a dispute now a matter of litigation involving the companies and citizens of gettysburg.

Maryland envirnmental employes conducted a preliminary analysis of the phosphorus, then called in EPA on april 4. Almost immediately, Tom Massey, EPA's "on-scene federal coordinator," assembled a team of 76 specialists.

"All the king's horses and all the king's men were brought together on this job," he said.

The EPA's assessment confirmed the worst. The "water over-packing" in the drums was interacting with the phosphorus to form phosphoric acid, whcih in turn was reacting with the metal of the drums to form hydrogen gas and phosphene gas.

By this time, the nation's attention was riveted to the events at the nuclear power plant in Pennsylvania. Few realized that the drama unfolding in Hagerstown also posed a grave danger.

"An explosion was possible, also the release of phosphene gas," said James L. Hearn III, Maryland's environmental enforcement official on the scene.

"There was a risk in moving it, but a greater risk in letting it stay there," said Massey yesterday, from Pittstown, Pa., where he is trying to avert another disaster involving deadly gas seeping from abandoned mines. "We couldn't even walk on the drums for fear of pressure on the hydrogen or phosphene gas."

While mapping out a 10-mile evacuation plan, Massey and others had to find a site and in the midst of a nationwide teamsters strike, people to drive the trucks.

The union agreed to provide drivers, at no charge, Massey said, but parts of the bureaucracy proved less cooperative. Massey declared the crisis imminent enough to make federal funds available, but where to truck the phosphorus was up to others.

No approved private sites were available for the chemicals. The Defense Department had sites but was reluctant to let them "become the dumping grounds for these types of programs," EPA's Jorling said.

"We and the governor of Maryland then embarked on an effort to get the White House to influence the Defense Department," he said. "It took better than part of a day and evening."

With Wihte House intervention, the military agreed to provide the A.P. Hill site if EPA assumed the liability, the expense and the general supervision. EPA was ready to move.

The convoy assembled shortly after midnight April 6 with fire trucks, sand trucks, two trucks carrying the phosphorus and a third in case one of the two broke down. They drove at night, Massey said, in part because they feared the heat of the sun could affect the cargo.

"We went interstate for continuity of motion," Massey said. "We didn't want to stop, herky-jerky." There were no sirens. "How did I do it? Very quietly."

If the phosphorus had ignited on the Capital Beltway, Massey said, phosphorus-fallout would have rained on parts of Washington. "My god, I'm telling you, I was scared," he said.

Also in the convoy were army explosives disposal experts and eight employes of an Ohio firm who were dressed in space age-looking suits, "in the event anything happened, to clean up or control the situation," Massey said.

The convoy arrived at its destination south of Washington as dawn was breaking. Over the next 12 days, each drum was moved individually onto an artillery range where, Massey said, "Thank God, we blew off 89 drums without incident."