INSTITUTE, W.Va. - Local residents say an emergency notification system failed its first major test at a Union Carbide Corp. plant after a choking cloud of gas rolled over four cities, injuring 136 people.

Six plant employees, one seriously injured, and about 130 nearby residents went to hospitals Sunday with lung, eye, nose and throat irritations after the leak of a chemical used to make pesticide. Thousands of people were asked to stay in their houses for several hours, until the chemical dissipated.

Carbide issued a statement today from company headquarters in Danbury, Conn., saying that "the emergency response system worked according to plan and all government authorities and hospital emergency rooms were notified in a timely fashion."

But local officials, emergency room doctors and residents injured by the choking fumes complained of inadequate warnings and information. Mayors of nearby communities including Dunbar, St. Albans, Nitro and Charleston said today that the information they received was too little, too late.

"The system didn't work," said Charleston Mayor Mike Roark.

Officials said the unit that produced the chemical, aldicarb oxime, was shut down following the leak, but that workers were on the job today in other parts of the plant.

The chemical cloud spewed from a unit that uses methyl isocyanate, the substance that leaked last December in the Indian city of Bhopal where more than 2,000 people were killed. Plant spokesman Henderson said the substance that leaked here, aldicarb oxime, is processed with MIC to make pesticides, but the MIC is consumed in production.

Henderson had earlier said aldicarb oxime was made from MIC, but he changed his account today. He also said today that the plant's MIC unit was never involved.

Company officials said a cloud of aldicarb settled on nearby homes after leaking from the plant when a gasket on a storage tank failed.

Many people living near the plant said their homes already were engulfed in fumes when they first heard the plant's emergency siren. "Carbide's got to do something better than this," said Donna Willis, one of nearly 300 residents examined at an emergency clinic.

"We can't let them wait 10, 20 or 30 minutes before they let you know what's going on. We could have been dead," she said.

The company said it notified the county Office of Emergency Services of the incident within "approximately five minutes" of the leak.

Henderson said the Carbide plant sounded a warning siren as soon as the leak was detected at 8:35 a.m Houston time.

But emergency personnel in Charleston, about 12 miles away, were not told, according to Roark.

"Each municipality is supposed to be notified," he said. "Our command center was not notified. Our public safety director heard it on the (police) scanner."

"If it had been something really bad, it would have been too late," said Vicky Terry, who said she awoke to find her home full of the stinging fumes. "People would have been dead in their beds," she said.

Reports of noxious fumes began spilling into radio stations about the time the leak was detected, said WCHS news director Mike Wilson. He said public notification was hampered because most radio and TV stations don't staff their news departments on Sunday mornings.

Emergency broadcasts beginning about 25 minutes later informed told Institute's 3 ,100 residents to remain indoors, close windows and shut off air conditioners. An all-clear was broadcast shortly before noon.

A Carbide statement said "an immediate investigation will be made to establish the cause of the accident and the quantity of material released."

At a news conference, doctors said most of the injured would recover quickly.

About 30 residents were admitted to hospitals with "mild to moderate injuries caused by irritant gases," said David Seidler, vice chief of emergency services for Charleston Area Medical Center.

Stanley Miller, 30, of Charleston, was listed in serious condition today while the others were satisfactory.

Aldicarb oxime is shipped from Institute to Union Carbide's plant in Woodbine, Ga., where it used in making Temik. Aldicarb sulfoxide was the pesticide that tainted watermelons in California earlier this summer, sickening hundreds.

The MIC unit at Institute was shut down after the Bhopal leak. It resumed production May 4 after installation of $5 million in new safety equipment.

The Environmental Protection Agency reported last Jan. 23 that safety records at Union Carbide's Institute, W.Va., plant indicated 28 leaks between 1980 and 1984 of methyl isocyanate. The EPA said it had not determined whether any of the gas spread outside the plant.