Advanced Genetics Sciences Inc. violated federal law by injecting a live, gene-engineered organism into trees on the roof of its headquarters before the government approved experiments to release the microbe into the environment, the Environmental Protection Agency said yesterday.

The company has been testing a laboratory-altered microbe called Frostban to be sprayed on plants to help prevent frost damage.

The EPA approved Frostban late last year for spraying on strawberries in an open field. But, beginning last Feb. 25 and continuing through the spring, the company injected the novel microbe into fruit trees on the two-acre roof of its Oakland, Calif., headquarters. The purpose was to see whether the microbe would harm plants and trees.

According to federal regulations, such tests are to be carried out in confined areas such as greenhouses to prevent the release of microbes into the environment. Released microbes might travel for miles if carried by insects or the wind.

The company's tests on trees were "an environmental release," the EPA said yesterday, because the injected microbes could leak out with the tree sap and be picked up by insects attracted to the sap.

John Bedbrook, AGS director of research, said Tuesday the company believed the rooftop experiment was "contained" because the microbes were kept in a syringe, then injected under the bark of the trees.

However, a substantial number of the more than 45 trees leaked sap where the syringe was inserted, the EPA said. In addition, three trees developed cankers, which suggested an adverse reaction to the microbe, a source familiar with the experiment said.

Spokesmen for AGS did not return telephone calls yesterday.

An EPA spokesman said the agency will notify the company in writing and will continue its investigation to determine what punishment, if any, to impose.

However, the EPA thinks the environmental risks are minimal, officials said, and they expect the company's strawberry field test to be approved eventually. The tests are being held up by local government officials in the Salinas region.

A suit against the EPA for approving the Frostban test is pending in federal court. The action was brought by activist Jeremy Rifkin and his Foundation on Economic Trends. A hearing is scheduled Friday.

Rifkin said yesterday that "AGS sent a message to the entire world that the industry is not to be trusted with the responsibility of policing itself."