The Department of Health, Education and Welfare is expected to release a statement tomorrow warning the nation's estimated 13 million marijuana users that irreversible lung damage could result from smoking Mexican marijuana contaminated by a highly toxic herbicide meant to eradicate it in a drug control program partially funded by the State Department.

Acording to studies conducted by HEW's National Institute on Drug Abuse, over 20 percent of the marijuana coming into the United States from Mexico may be contaminated with the herbicide, paraquat, in amounts of over 2,200 parts per million.

The maximum level of contamination on food crops permitted for use in this country is 0.05 parts per million. "Since approximately 60 percent of the marijuana consumed in this country is of Mexican origin," the report said, "this represents a large exposure population."

What paraquat does specifically, according to the NIDA study, is to "concentrate in the lung tissue and produce a condition called fibrosis, which effectively reduces the capacity of the lung to absorb [WORD ILLEGIBLE]

Since the chemical turns marijuana a yellowish-gold in color uninformed users easily could confuse the contaminated marijuana with high-quality marijuana, known popularly as Acapulco Gold.

"Some people are going to take one look and think it's top of the line," said Keith Stroup, president of the National Organization for the Reform of Marijuana Laws (NORML).

NORML said yesterday it plans to file suit Monday in U.S. District Court here to end U.S. support of the spraying program.

Despite the highly toxic nature of the herbicide, one State Department official said that no recommendations will be made to Mexico concerning continued use of paraquat. "We will of course share this information with the Mexican government," said Mathea Falco, who supervises the State Department's International Narcotics Program. "But it's their program and their country. It's up to them."

According to Falco, $13 million a year is given to Mexico to "help in drug eradication and control" in a program to which Mexico contributes $40 million. Most of the U.S. money, he said, is spent on the eradication of Mexican opium poppy fields in an attempt to reduce the amount of heroin, an opium derivative that is smuggled into the United States.

Once the poppy season ends in the summer, however, said Falco, American helicopters spray equipment and personnel are used on the marijuana fields.

Paraquat will decompose marijuana plants within three days if they are exposed to direct sunlight, but Mexican marijuana farmers, in an apparent effort to salvage their investment before the daylight deadline beats them to it, are harvesting the plants immediately after they have been sprayed. Once packaged, the marijuana is safe from further decomposition.

Question about paraquat's possible harm were first raised by Sen. Charles H. Percy (R-Ill.) in a letter to Secretary of State Cyrus R. Vance 10 months ago. After a meeting called by the White House Office on Drug Abuse Policy last May, tests on the paraquat-tainted marijuana were ordered by Peter Bourne, the office's director.

In a letter to Bourne Thursday, Percy said the government should "undertake immediately to safeguard the health and welfare of a significant number of our citizens who may be endangered as a result of this government's involvement, however direct or indirect, in Mexico's program to spray marijuana fields with paraquat."

A spokeswoman for Bourne's office said yesterday, however, that Bourne had not yet read the Percy letter. Nevertheless, she said, paraquat "is not a drug policy issue, but a health issue."