The incinerator ship Vulcanus, once used to destroy leftover Vietnam defoliant Agent Orange, will begin to burn 3.6 million gallons of oil full of dangerous PCBs in the Gulf of Mexico next week under a controversial research permit usually given only to small-scale test projects.

Until last week, the October permit to Chemical Waste Management Inc., of Oak Brook, Ill., had no requirement that the burn be proven effective until more than half of it was finished.

That was "an oversight," said Environmental Protection Agency official T. William Musser, and will be remedied in an amendment going out this week. The amendment will allow 850,000 gallons to be burned before the ship's "destruction efficiency" is certified, an amount that still alarms some competitors and environmental groups.

The 334-foot ship, a converted tanker, has never before tried to destroy PCBs (polychlorinated biphenyls), which are highly stable and hard to burn. The oil is also contaminated with dioxin, one of the most deadly substances known.

Critics worry that PCBs escaping into the air from incomplete burning could be carried by the prevailing Gulf winds from the burn site in the middle of the Gulf about 350 miles southwest of Mobile, Ala., to populated areas, possibly endangering the health of millions.

But Musser, a physical scientist in the EPA water office's marine protection branch, said the agency is confident that the ship will handle PCBs as well as it did Agent Orange, which is also contaminated with dioxin. Another EPA official said the burn area was chosen because the winds there should not carry the PCBs over land.

"The only reason it's a research permit is that PCB burning hasn't been done before on the Vulcanus," Musser said.

Donald Carruth of the American Eagle Foundation, a small environmental group of retired government officials, called the situation "a slapdash arrangement" in which there is no evidence of its competence.

"We're concerned that it be absolutely and thoroughly checked before this begins, and that a full complement of monitoring personnel go along," he said.

EPA sources suggested that the firm was unwilling to commit the ship and its 18-member crew to the 10-day round-trip travel time to the Gulf burn site and a 10-day burn period without a guaranteed payload big enough to make a profit.

Company spokeswoman Paula Waters said the firm is charging businesses that own the PCB oil $3 to $7 per gallon to take care of it. At that rate the permit is worth $10.8 million to $25.2 million.

EPA banned PCB production in 1979 and prohibited its disposal in landfills last year. But millions of old electrical transformers and capacitors containing PCB-laden oil are either still in use or stored in warehouses nationwide, awaiting a large-scale disposal method.

Only two companies are now licensed to deal with PCBs, both on a scale of about 200,000 gallons per month: Energy Systems Co. (ENSCO) in Arkansas and the Rollins Corp. in Deer Park, Tex.

The Vulcanus' permit amendment will require that the ship's "destruction efficiency" be validated at the end of its first trip to the Gulf before the burn can proceed, Musser said.

At that point the ship will have burned about 850,000 gallons of the PCB-contaminated oil. Three more trips would be needed to complete the 3.6-million-gallon project.

An EPA inspector and an independent monitoring firm will be on the vessel to watch its "combustion efficiency," or output of carbon and other chemicals, with authority to halt the burn at any time, Waters said.