In a makeshift compound of borrowed trailers here, a 25-member team of medical specialists began today to seek clues to one of the most puzzling and troublesome legacies of the Vietnam war.

Experts from New York, Ohio and California flew in after alarmed Arkansas officials put out a call for help when they found traces of a deadly pesticide contaminant known as dioxin leaking from a small chemical plant here. The plant is owned by the Vertac Corp.

State and federal investigators have taken samples containing dioxin from a creek, a nearby bayou, the city's sewage treatment plant and several vegetable gardens just outside the gates of the 93-acre Vertac plant.

This morning teams of white-coated doctors began examining the first of about 150 persons - many of them past and present workers at the pesticide plant - to determine if their exposure to the herbicide 2,4,5,-T during its manufacture has caused any physical damage.

Nearly all 2, 4, 5-T contains some dioxin, which is produced during the manufacturing process.

While the immediate question is the amount of harm that workers and other residents living near the plant may have suffered from dioxin, Dr. Irving J. Selikoff, the head of the medical team, said the examination will help solve a more far-reaching problem.

Selikoff, director of the environmental science laboratory at the Mount Sinai School of Medicine in New York City, said the examinations will be used to begin assembling data to determine whether dioxin is, in fact, as often has been asserted, among the world's most hazardous chemical compounds.

Some researchers contend that dioxin causes cancerous tumors in test animals in concentrations of as little as five parts per trillion - an amount that barely can be detected by even the most sophisticated laboratory equipment. Other experts contend warnings about dioxin in 2,4,5-T are overblown, and the danger from the compound is unproved.

"We desperately need the base of factual information we're getting here," Selikoff said. "The implications of what we're doing here will be felt through the country and the whole world."

The most heated and potentially wide-ranging controversy over dioxin flared last year when hundreds of Vietnam veterans filed lawsuits against manufacturers of 2,4,5-T. The veterans claimed that they were exposed to dioxin when they were sprayed with 2,4,5-T during the Vietnam war, and that many are now developing nervous disorders and other problems.

When experts examined leftover supplies of Agent Orange after the Vietnam war, they found between 0.5 and 20 parts per million of dioxin contamination.

The veterans administration and the chemical manufacturers have countered the claims, saying there is no medical evidence to substantiate the charges.

Between 1961 and 1970 the Defense Department sprayed millions of gallons of te herbicide - calling it Agent Orange - ove rjungle canopies in Vietnam during defoliation efforts. The spraying was halted when pregnant Vietnamese women exposed to it began having children with birth defects.

The veterans' claims are particularly relevant here. Between 1965 and 1971 the Hercules Powder Corp. was one of the leading manufacturers of Agent Orange. The company made more than 14 million pounds of the herbicide for the defense Department at the plant here. Vertac purchased the plant here. Vertac purchased the plant from Hercules and continued to make 2,4,5-T up to this year.

Last month Arkansas Health department officials found 13 of 74 current employes at Vertac showed some signs of chloracne, a disease generally caused by exposure to dioxin.

When the Mount Sinai team opened for business here at 8 a.m. today a small line of workers already had formed outside the Pulaski County health unit, where the tests are being run.

"We just want to be sure nothing is wrong," said Cathy Blue, from Cotton Plant, Ark. Mrs. Blue jiggled her 3-month-old daughter in her arms as she stood alongside her husband, Larry, who worked in the plant in 1973.

"I don't remember anything wrong with him," she said. "But he'd come home and his clothes stunk something pitiful. Sometimes I couldn't even get near him."

The medical team will spend three days here testing workers and others for signs of dioxin problems. In addition to skin tests the researchers are running tests for brain and nerve problems and looking for signs that the chemical may interfere with normal disease resistance.

Selikoff said some test results would be available almost immediately; other tests could take up to a year to analyze.

Earlier this year a similar Mount Sinai team examined former pesticide workers at a plant in Nitro, W.Va., where the Monsanto Chemical Co. made 2,4,5-T until 1969.

Concern over the dioxin situation here is particularly acute. Gov. William Clinton has opposed efforts by Vertac to resume immediate production of 2, 4, 5-T and state officials have called the dioxin leak the state's worst environmental disaster.

Clinton's position has not been helped by the fact that Arkansas rice growers - the state's largest agriculture bloc - are heavy users of 2, 4, 5-T. But the governor said yesterday that he would not favor resumption of 2, 4, 5-T production by Vertac in the state until the medical questions about dioxin have been answered.

"Our attitude in this state has shifted markedly because of our experience here," said the governor. CAPTION: Picture, Vertac Corp. plant in Jacksonville, Ark.: 2,4,5-T, a Vietnam defoliant containing the deadly contaminant dioxin, was made here from 1965 until this year. AP