BY TIM JOHNSON

  WASHINGTON - The Bush administration told Congress on Thursday that its program of aerially spraying herbicide on coca crops in Colombia may cause eye irritation to farmers on the ground but poses no other significant health or environmental risks.

  The 180-page report, which watchdog groups criticized as flawed, came as U.S. officials hope to intensify aerial spraying in Colombia to battle the illegal narcotics
  industry.

  ''We believe that this is an extremely important program and that we will achieve positive results by the end of the year,'' said Paul Simons, acting assistant secretary of state for international narcotics matters.

  MEETS U.S. STANDARDS

  The State Department report certified that Secretary of State Colin Powell had found that chemicals used in the U.S.-financed aerial eradication program pose no
  ''unreasonable risks or adverse affects'' to humans or the environment in Colombia.

  It said the program meets U.S. regulatory standards and is conducted in a way to address complaints of citizens who claim their health or their crops have been harmed.

  The aerial spraying has generated more than 1,000 complaints from Colombians who say their food crops have been damaged or their health affected by the herbicide.

  SENATOR CRITICIZES

  Since 1994, U.S. officials have financed efforts to spray a substance containing glyphosate -- the most widely used conventional herbicide in the United States -- on illegal coca and poppy crops in Colombia.

  While other countries in the Andean region prohibit the aerial spraying, it has become a cornerstone of U.S. anti-drug efforts in Colombia, source of most of the world's cocaine.

  Sen. Patrick Leahy, a Vermont Democrat who sponsored the language requiring the State Department to certify the safety of the program, assailed the report.

  ''Spraying a toxic chemical over large areas, including where people live and livestock graze, would not be tolerated in our country. We should not be spraying first and asking questions later,'' Leahy said.

  'MINIMAL' RISKS

  The State Department report included separate assessments by the Department of Agriculture and the Environmental Protection Agency.

  ''Glyphosate poses minimal health risks to humans and animals, is environmentally benign, and degrades rapidly in soil and water,'' Agriculture Secretary Ann M.
  Veneman said in a letter to Powell included in the report.

  But the EPA was far more cautious, even critical in its assessment, noting that it had not been able to conduct direct research in Colombia and relied only on data
  provided by the State Department, which is deeply vested in the success of ongoing counter-narcotics programs.

  DIFFERENT REACTIONS

  Aerial application of the herbicide and inert substances that help it stick to the waxy leaves of coca plants may cause ''acute eye irritation'' in humans, drift on to
  ''non-target plants,'' and have different reactions in Colombia's tropical ecosystem than in the temperate climates of the United States, the EPA said.

  A State Department official said the U.S. Embassy in Colombia later this month would change the composition of the herbicide it uses to lessen possible eye irritation.

  Under current conditions, the eye irritation experienced by some farmers is ''as if you had baby shampoo in your eyes,'' the official said. ``It goes away after 72 hours.''

  DRAWBACK

  The Amazon Alliance, a coalition of environmental and indigenous groups, said the EPA's lack of access to data from Colombia on actual conditions is a major drawback to the study.

  ''How much can this analysis tell us? It would be like asking a car mechanic to check your oil, and not letting him open the hood,'' said Betsy Marsh of the Alliance.

  MORE PLANES

  U.S. personnel currently oversee 15 crop-duster aircraft in Colombia, and three more should arrive by the end of the year, a State Department official said.

  Eradication efforts will soon increase.

  Marc Grossman, the State Department under secretary for political affairs, said in mid-August that the U.S. program hopes to spray a record 150,000 hectares of coca this year, nearly double the 84,000 hectares sprayed last year. (A hectare is equivalent to about 2.47 acres.)

  ''There's no way that alternative development is going to be ratcheted up to meet that. I think you'll see more displacement of people,'' said Lisa Haugaard of the Latin America Working Group, a liberal watchdog group in Washington.

  Grossman said two weeks ago that 11,000 families are registered to receive help from U.S.-financed alternative development programs to stop growing coca.