More than a dozen members of Manuel Costa's family had gathered at Glover Archbold Park to celebrate his 44th birthday Sunday, when his wife, Alda, strolled into the nearby woods to gather kindling for the fire to cook the Portuguese-style chicken she had prepared.

Moments later, Alda Costa returned to the picnic tables looking pale and weak, complaining that she had been stung by something--probably a bee--twice in the back, once on the leg and once on the finger.

Her family sat her down and rubbed vinegar on the bites, but Costa blanched, gasped "I'm very sick," and then toppled from her chair, according to her husband.

Manuel Costa rushed his wife to Sibley Memorial Hospital, but minutes later, Alda Costa was dead, the victim of a rare allergic reaction to an insect sting, according to Dr. Stuart Dawson, D.C. deputy medical examiner.

"They told me it was a one-in-a-million case," Costa said yesterday. "They said there was nothing they could do to save her life."

The death was one of an estimated 20 to 50 per year nationwide that are attributed to insect bites, according to entomologists, who said that although snake bites get more publicity, insect bites kill far more Americans. The death was apparently the first of its kind in the District in the last five years, according to the medical examiner's office.

Costa, a construction worker from Chevy Chase, spent much of yesterday arranging for passports for his son, Carlos, 11, and six other members of the shocked family to accompany the body back to Braga, Portugal, for the funeral of his 41-year-old wife.

"Nobody knew the bees were there," Manuel Costa said yesterday. "She just came up and said, 'I got stung pretty bad.' . . . And then she just lost all her strength. She stopped breathing. I tried to give her a cup of water, but she couldn't breathe. She couldn't swallow."

Costa estimates he got her to Sibley within five minutes, "but when we got there, she had just passed away."

"A surprisingly large number of people die from the bites of arthropods insects and spiders and from bees in particular," said Ronald McGinley, associate director of entomology at the Smithsonian Institution, who has lectured on insect bites. Bees are the most frequent culprit in insect-bite deaths, followed by yellowjackets, wasps and hornets, according to medical studies.

Alda Costa's death, according to the medical examiner, was caused by a severe allergic reaction to the insect's venom, which triggered a sudden drop in blood pressure and led to her death. The autopsy showed no other health problems.

The kind of allergic reaction Costa sustained, according to McGinley, is generally caused when a person suffers an earlier sting and the exposure to insect venom causes a hypersensitivity to subsequent stings.

"If you are stung once, it will not kill you" usually, McGinley said. "But after the second bite, you can have a major reaction" that can be fatal within minutes. "You can get stung once and not know whether you are allergic. And then you get zapped the next time, and you drop dead," he said.

Dr. Page Hudson, the chief medical examiner of North Carolina and an authority on insect bites, said a tiny percentage of the population, "maybe one in 10,000," develop a "super-allergic" fatal reaction to insect venom.

In most cases, people learn they have a tendency toward severe reactions when they get swelling and pain at the site of the bite, Hudson said.

"Once you know you are hypersensitive, you should either carry adrenaline or antihistamines, or you should seek out being desensitized," he said. Desensitization is a process in which patients are given small, but steadily increasing doses of venom to help their body develop immunity to the irritant, he said.

Many people who are allergic to bites carry a kit to give themselves antihistamine or adrenaline injections, he said.

A veteran beekeeper, Harold Liberman, who runs the Free State Bee Service in Upper Marlboro, said yesterday that bees rarely attack unless disturbed. In most cases, ground-nesting bumblebees or yellowjackets live in old tree stumps and attack if someone blunders into their nests, he said.

Three years ago, a 50-year-old beekeeper in Silver Spring dropped a beehive he was unloading and was stung by hundreds of bees who swarmed under his protective gear. He died two hours later.

For those who fear bee stings, experts advise not to wear perfumes or brightly-colored clothes and to be careful not to disturb insect nests.

Alda Costa came to the United States from Portugal and worked for several years at the Brazilian Embassy as a domestic, her husband said. The couple met in Portugal in 1964, and he joined her here in 1966, when they were married. "She worked in the house since then . . . and now we have to carry on without her," her husband said. "We have to struggle along."