An advisory panel is expected to give conditional approval today to the third and most scientifically controversial attempt to take a live, genetically engineered microbe out of the laboratory and into the field.

The panel of outside experts, called the Scientific Advisory Panel, will officially report to the Environmental Protection Agency that an experimental test permit should be given to Monsanto Agricultural Products Company, provided further tests are carried out satisfactorily.

The product Monsanto wants to test in a small field experiment near St. Louis is a bacterium that would live near the roots of corn and exude a pesticide to kill larvae attempting to attack the corn plant.

It is the first case in which the government has considered putting a new poison-producing microbe into the environment. The bacterium, called Pseudomonas fluorescens, has been altered by the insertion of a gene from another bacterium, a gene that produces the pesticidal chemical.

Regulating releases of gene-engineered products into the environment has so far been plagued by problems.

The EPA determined that one company, Advanced Genetic Sciences of California, broke the law in testing its frost-preventing microbe. The Department of Agriculture failed to provide the necessary environmental assessment before allowing distribution of a genetically engineered vaccine, then withdrew the vaccine from the market for two weeks, and faces court action over its handling of the case.

The Monsanto case is the third product to move through regulatory agencies and is the most controversial scientifically because the bacterium produces a poison which will kill some living things, and which may remain for some time in the soil before dying.

The EPA's Hazard Evaluation Division issued a report on March 26 stating that many of Monsanto's safety tests were defective and useless in determining the risk of putting the organism into the field.

The report listed tests that it said should be repeated before a permit should be given. For example, in determining whether the pesticide from the organism would hurt fish, Monsanto tested the pesticide for only four days. The EPA group said that was too short an exposure to determine if the fish would be harmed.

The Scientific Advisory Panel is expected to agree that many tests must be repeated to clarify how the new microbe will spread and whether it will harm other species besides the larvae it is intended to kill. But the panel also has said that questions of risks have been answered in general but more accurate testing is needed.

The EPA will consider recommendations from its evaluation division and the outside advisory panel before issuing a field test permit and listing restrictions. A decision is expected by mid-May.