Sunday's toxic gas leak at the Union Carbide plant in Institute, W.Va., represents a serious public relations setback for the corporation, which is still trying to recover from a disastrous leak last December at its virtually identical plant in Bhopal, India.

An estimated 2,000 people died when methyl isocyanate (MIC) leaked from the Bhopal plant in the worst industrial accident in history. Since then, Union Carbide has reeled under stinging public criticism, a sagging stock price and more than 100 lawsuits filed in U.S. courts asking for billions of dollars in damages.

The company, based in Danbury, Conn., has made huge investments in new safety equipment, including $5 million at the Institute plant, in an attempt to soothe public concerns about its chemical operations. It also has sought to blame sloppy Indian management or, more recently, sabatoge by Sikh terrorists for the Bhopal leak. Yesterday, critics said the escape of toxic gas from the Institute plant punctured major holes in the company's credibility and raised new questions about its claims that an accident as serious the one in Bhopal could not happen in the United States. Six company employes and 136 Institute residents were injured in a leak of aldicarb oxime, an MIC derivative used in manufacturing pesticides.

According to Michael Ciresi, a Minneapolis lawyer representing the Indian government, the new incident also could bolster a recent motion by India and other plantiffs to begin discovery in the Bhopal lawsuits, which have been consolidated in federal court in New York. The motion is aimed, in part, at exploring design similarities between the Bhopal and Institute plants.

"This shows the utter falsity of their statements that Bhopal was the result of sabatoge," Ciresi said. "That is utter nonsense. What it does show is that the system they have in place is defective. This incident focuses attention back on the conduct of Union Carbide."

Carbide officials dismissed such claims and insisted that the aldicarb-oxime leak was not remotely as serious as the MIC cloud in Bhopal. Carbide spokesman Earl Slack initially contended that the company's emergency response system "worked according to plan." Company officials later revised the statement, saying they had waited 20 minutes to notify officials because they believed that the leak had been confined.

The plant, in an area sometimes called the nation's "chemical capital," is the only U.S. facility that produces MIC. Carbide shut down MIC production there immediately after the Bhopal accident, resuming May 4 after putting in new scrubbers, flares and other safety equipment, hiring outside safety consultants and installing a new emergency response system to alert area residents of possible danger.

"We've looked at this facility with a fine-tooth comb," Carbide spokesman Thad Epps announced at a news conference before the plant reopened. "We know the whole world is watching what we're doing." In the face of the leak and the delayed alert, Carbide found itself under attack yesterday from local officials who had long supported the company. Charleston Mayor Mike Roark, who had endorsed the resumption of MIC production, said that "the system didn't work" and that "there are serious questions and gaps in their credibility."

"People here are very apprehensive that if they're too hard on Carbide, Carbide will go to the Sun Belt or the Third World," said Perry Bryant of the West Virginia Citizens Action Project. "But there's all kinds of contradictions in what they've been saying. They told the community not to be concerned, they would sound the alarm system in plenty of time for people to evacuate. But that didn't happen."