BALTIMORE, NOV. 13 -- Two years ago, when federal law first required industries to disclose how much pollution they released into the air, water and land, environmentalists took aim at south Baltimore's chemical corridor.

Today, 11 of those chemical plants attempted to seize the high ground by announcing that by the end of this year, they will have reduced total toxic emissions 74 percent from 1987 levels. That includes a 79 percent decrease in water toxins, 68 percent in air toxins, and 61 percent in toxins in landfills.

"We're not done yet," said Louis H. Kistner, president of the Chemical Industry Council of Maryland, a trade group representing the companies. "By assembling the data we recognize . . . we have further to go."

Company spokesmen said well over half the reductions were voluntary and do not reflect declines in production, although some were made in anticipation of new state and federal laws that will restrict air and water pollution.

Local environmentalists reacted with surprise to today's announcement, saying they did not have enough information to judge the chemical companies' claims. Some questioned whether the reductions resulted from bookkeeping changes, but Kistner said industry did not "fuzzy the numbers in any way."

"Thanks a lot, but you still have a long way to go," said Mary Rosso, president of the Maryland Waste Coalition. Rosso, who lives a mile or two from several south Baltimore chemical plants, said that despite the reductions, "It's really hard to breathe in this area at certain times."

Today's announcement, made at the squat beige W.R. Grace plant on Chemical Road, reflects a change in the industry's public posture since the so-called federal right-to-know law began requiring companies to issue annual reports of major emissions of more than 300 chemicals.

Then, when environmental groups said the total tonnage was unacceptable, many companies reacted defensively, pointing out that the releases were entirely legal and accusing critics of exaggerating their potential dangers. Today, Kistner acknowledged that the public reaction to the reports also was a "kicking-off point . . . . We're not going to be doing well if we report an ongoing increase."

The charts released today did not list specific chemicals, but industry spokesmen said they included major cuts in benzene, which is a carcinogen, as well as ammonia, sulfuric acid, hydrochloric acid, metals, chloroform and formaldehyde.

The companies that touted their emissions reductions include some of the giants of Maryland's chemical companies, the state's seventh largest industry -- FMC Corp., SCM Chemicals, and W.R. Grace & Co. They are among the state's biggest polluters, but several other large companies -- Bethlehem Steel and Westvaco paper -- are not included in the chemical group's figures.

All except one are currently in compliance with Maryland environmental laws, and that one -- Rhone Polenc -- is expected soon to sign a consent order spelling out how it will comply with Maryland's air toxics law that took effect this year, said Michael Sullivan, spokesman for the state Department of the Environment.

Five of the others -- FMC, SCM, Vista Chemicals, Atochem North America and W.R. Grace -- already have signed consent orders or agreements to bring themselves into compliance.

The other firms include Chemetals, Courtney Industries, Delta Chemicals, Peridot and Reichhold Chemicals.

Some reductions were achieved by spending millions of dollars on pollution controls such as scrubbers on smokestacks. Others resulted from changes in production, such as substituting less toxic substances or recycling contaminants instead of throwing them away, industry spokesmen said.

The 11 companies have invited south Baltimore residents and officials to a meeting from 7 to 10 p.m. Wednesday at St. Athanasius Church to talk about pollution reductions, and some will hold open houses in the spring.