Jay Feldman, coordinator of the National Coalition Against the Misuse of Pesticides, said: ''The other two chemicals don't have the same restrictions, but while that may be complying with the letter of the law, it is violating the principles that protect national lands to ensure the protection of wildlife habitats and recreation areas.''

Under a consent decree resolving the 1983 suit by several environmental groups and the National Organization for the Reform of Marijuana Laws, the D.E.A. agreed not to spray paraquat until after the Government prepared a statement on the action's effect on the environment.

The impact statement was completed in July 1985 and found that ''there is a slight risk that heavy smokers of marijuana could be affected by paraquat-sprayed marijuana.'' The document also opened the way for use of glyphosate and 2,4-D.

Glyphosate, a weedkiller like paraquat, was first used in September 1985.

Paraquat, which is used in agriculture to clear fields before planting and after harvest, is an acid that can produce severe lung damage in humans if ingested.

The Government contends that while paraquat is dangerous in a concentrated form, once it is sprayed it becomes ''biologically inactive.''