Howard County, known for its rural charm and exurban affluence, also boasts an unlikely wealth of something not so charming: toxic chemicals.

According to a report released recently by an environmental group, companies in Howard routinely release more toxic chemicals into the environment than do businesses in any other county in the Washington region.

Howard's total release in 1988 of 340,000 pounds of toxic materials into the air, water and land was higher than that of any of the other jurisdictions studied in the region. Citizen Action, an environmental watchdog group, examined the city of Alexandria and Arlington, Fairfax, Howard, Montgomery, Anne Arundel and Prince George's counties, which released a combined total of 711,832 pounds of toxic chemicals.

Although the releases are not illegal -- in some cases the government does not regulate the chemical involved -- the group that compiled the report from U.S. Environmental Protection Agency data urges the companies to reduce voluntarily their toxic discharges.

"In some cases, these substances are linked to cancer, to birth defects and other health problems," said Ed Rothschild, a spokesman for Citizen Action, which compiled the report "Poisons in Our Neighborhoods."

"It's got to improve the public health to minimize these things," said Rothschild, whose group is urging the corporate community to halve its emissions within five years.

Officials of some of the companies in the study said they have already discontinued use of the chemical listed or are looking for less toxic substitutes. The firms releasing the toxic chemicals manufacture everything from polymers for automobile undercoating to powdered milk.

The authors of the report caution that the EPA data they used do not include some major sources of pollution such as utilities, small employers and gasoline stations. The authors note that toxic materials such as benzene, from automobile emissions, and organic compounds, from lawn chemicals, are also major sources of pollution.

In Howard, the largest releases came from a facility that is no longer in the county, the General Electric Co.'s appliance plant in Columbia. The plant closed this summer after the company moved its appliance operations out of state. In 1988, GE reported releasing more than 82,000 pounds of materials at the Columbia site, primarily into the air. The substances included trichloroethylene, a carcinogen, and methyl ethyl ketone, which has been found to cause birth defects in animals, according to Citizen Action.

The company, which manufactured refrigerators, stoves and other appliances, also released nitric, sulfuric and hydrochloric acids, nickel compounds and ethylene glycol.

Several companies involved in making dairy products are high on the list, including Maryland and Virginia Milk Producers in Laurel, which released more than 81,000 pounds of nitric and phosphoric acid. The company, which processes milk into butter, nonfat dry milk and other products, uses the acids to clean equipment and lines, according to George Walgrove, manager of the manufacturing division. The acids are spread on fields on the premises, he said.

High's Dairies, which is owned by Texas-based Morning Star Foods Inc., reported releasing into the air 70,900 pounds of ammonia at its Whiskey Bottom Road location and more than 9,000 pounds at its Laurel location. Company officials could not be reached for comment.

Davis & Hemphill, a machine-tooling job shop in Elkridge, estimated that it released 54,000 pounds of trichloroethane into the air. The company uses the chemical as a degreasing solvent to clean production equipment, according to the company treasurer, Francis Duncan. Breathing trichloroethane can cause dizziness, irregular heartbeat or death, according to Citizen Action.

Chesapeake Finished Metals, a metal-finishing plant in the Dorsey area, released more than 25,000 pounds of toxic material, primarily into the air, but also into the public sewerage system, according to the report. The largest component of that release was xylene, which has been linked to birth defects, the report said. Also about 750 pounds of chromium, lead and zinc compounds were released into the public sewerage system, and more than 20,000 pounds of those three substances transported to disposal facilities.

The W.R. Grace Co. research facility in Columbia reported releasing 750 pounds of methyl ethyl ketone, the report said. The solvent was used in the process of developing a polymer undercoating for cars -- a project that has now been completed, according to Joseph W. Raksis, vice president for organic polymers for W.R. Grace's Washington Research Center. (Raksis said the company actually reported its releases of the solvent to be 500 to 1,000 pounds.)

M.G. Industries, a manufacturer of compressed gases that operates a plant in Jessup, is listed as releasing 250 pounds of acetone into the air. A company spokesman disputes that figure, noting that the company estimated emissions in the range of one to 499 pounds. "The actual release is probably no more than five pounds," said Anthony J. McErlean, manager of loss prevention and regulatory affairs. The acetone is used as a stabilizer in the manufacture of acetyline cylinders, he said.

Wilkins Rogers Inc., the flour mill in Ellicott City, released 23 pounds of chlorine into the air, according to the report. The chlorine is used to kill micro-organisms in wheat, according to Debbie Taylor, quality control manager.

Hittman Materials and Medical Components Inc., of Columbia, was listed as releasing 12 pounds of ammonia into the air. Company officials could not be reached for comment.