A California teen-ager has won an $8.3 million out-of-court settlement from Conrail, three years after he was severely burned by a high-voltage wire an an open Conrail yard in Southwest Washington and was left a triple amputee.

The settlement, believed to be one of the highest personal injury awards in the country, will be paid to the youth, Steven Throop, 16, over the course of his lifetime in a combination of monthly payments, special bonus payments every five years, and a separate $500,000 trust fund, according to Throop's lawyers. All of the award is tax free except for the trust fund, which he cannot use until he is 35.

Throop was injured in 1978, during a family vacation to Washington, after he climbed on top of a parked railroad car on the single track at 7th and D streets SW to get a better view of the annual July 4 fireworks show on the Mall. Throop, then 13, either touched an 11,000 volt wire that was hanging just a few feet above the boxcar or walked within the wire's electrical field.

Throop's lawyers contended that Conrail was negligent since there was no fence around the railroad property, no warning of the high-voltage wire, and only faded, stenciled "No Trespassing" signs on poles to warn intruders.

In addition to the $8.3 million Conrail agreed to pay Throop, the railroad company also will pay $750,000 to the San Jose, Calif., law firm headed by James F. Boccardo, which specializes in negligence cases and represented Throop; $150,000 to Thomas M. Rees, the firm's Washington lawyer and a former California congressman, plus all court costs.

Conrail is a quasi-federal agency that operates freight trains and a few passenger trains. It is heavily subsidized by federal taxpayers.

"It is cheaper for them to defend these lawsuits, even paying the same kind of money they paid [Throop], than to upgrade the property," said Richard Alexander, one of the attorneys for Throop. "I wish they would put some money in prevention [of accidents] -- at least a sign."

Conrail spokesman Bill Watson of Philadephia confirmed that there had been a settlement with Throop, but declined to discuss details of the financial arrangement. Wilson said that, as a policy, Conrail puts fences only around railroad yards, not single tracks like the one that runs through the vacant lot where Throop was burned.

That track in Southwest Washington -- where boxcars occasionally are parked -- was the scene of an earlier mishap in 1971, when 14-year-old Preston Morris of Northwest Washington was killed and a D.C. police officer, Sgt. Raymond Zilko, was severely injured trying to retrieve his body.

Following the 1971 incident, the National Transportation Safety Board issued a report criticizing Penn Central, which at that time owned the track, for not fencing the area and posting adequate warnings.

Throop underwent about a dozen operations after his accident, according to Rees. Throop's right arm eventually was amputated just above the elbow, and both legs were amputated above the knee.

Rees said that Throop, whose parents are divorced, went through serious emotional problems readjusting to life as an amputee. Formerly athletic and outgoing, he has gained considerable weight, a problem that Rees said is not uncommon to persons confined to wheelchairs who are unable to exercise very much.

During his rehabilitation, Throop passed a California examination to earn the equivalency of a high school diploma and now is enrolled at Cabrillo Junior College, studying marine biology. Alexander said that the youth hopes to spend part of his money continuing his studies at UCLA.

Under terms of the complex financial award, Throop, who now lives in a foster home, will receive $2,250 each month beginning in June and continuing for the rest of his life. His lawyers estimate that those monthly payments ultimately will total $5.4 million. Those payments include a built-in inflation factor.

In addition, Throop will receive bonus payments, starting with $25,000 five years from now and another $50,000 in 10 years. Those bonus payments are scheduled to increase every five years, so that by the year 2036, he will receive a $275,000 bonus check. Those payments are estimated to total $1,625,000 during Throop's lifetime.

The trust fund will be administered by Rees in Washington for use in emergencies, such as an unexpected medical problem. Alexander said that the remainder of the award will be raised through investment of the money as Throop receives it.

The lawyers said they preferred the out-of-court settlement to a jury trial here, because of the unusually large amount offered and because court rules in the District make it more difficult to prove negligence than in most jurisdictions.