Children in thousands of public schools across the nation may be exposed to cancer-causing asbestos, the Environmental Defense Fund said yesterday.

The fund, an environmental group of 45,000 members, filed a petition with the Environmental Protection Agency demanding that EPA identify all public schools where asbestos is a hazard and require asbestos manufacturers to make necessary repairs.

The National Education Association, the National Parent and Teachers Association and the American Federation of Teachers also called for immediate action.

"Not only is the health of children at stake but also that of teachers, para professionals and other staff who are likely to spend many more years working under potentially hazardous conditions," said AFT President Albert Shanker.

Asbestos was frequently sprayed on ceilings and walls for insulation, fireproofing, noise control and decoration until such uses were banned in 1975. A fibrous whitish mineral, asbestos has been shown to cause cancer and respiraatory problems even where exposure is limited.

In the last few months, about 6,000 of the nation's 87,000 schools have been inspected. Almost 1,000 have been found to have harzardous amounts of asbestos in the ceilings or in the air, according to an EPA survey.

Ney York city school board official Fern Lapidus, who attended the fund's press conference yesterday, said the city has surveyed its 1,000 schools and that asbestos is being found in a third of them. Two Harlem grade schools have been closed and 300 students transfered to other schools.

The District of Columbia has examined its 193 schools. Eight were found to have some asbestos on the ceilings or walls. Three schools have been repaired so far, schools officials said.

However, 25 states have inspected less than 1 percent of their schools, according to EPA.

"Millions of students are potentially exposed," said defense fund attorney Robert Rauch, "and yet EPA has completely failed to address the problem." The fund has been prodding EPA for six months without success, Rauch added. Yesterday's petition will allow the fund to go to court in 90 days to try to force the government to act.

However, EPA Assistant Administrator Steven Jellinek said the agency is developing a technical assistance program to help schools identify and correct asbestos problems. The program will be in operation in a few weeks, he added, as soon as manuals are printed.

"We think our approach will result in faster action," Jellinek said. "If it doesn't, then we will consider regulations" as the fund has petitioned. He added that the agency prefers to ask schools, rather than asbestos manufacturer Johns-Manville Corp., to pay for repairs.

Children are particularly vulnerable to asbestos because they breathe more air and have a longer life span to develop slow-growing cancers, Rauch said. The risk of asbestos-caused cancer is greatly increased by smoking and eight million teen-agers smoke, he added.

However, public schools are "only the tip of the iceberg," Rauch said.Other public buildings, private schools, public and private universities and office buildings across the country were extensively sprayed with asbestes, Rauch said.

The most significant hazards occur during routine building maintenance, such as repairing electrical fixtures. When the asbestos is cut, the dust and flakes get into the air and are recycled continually.

Fund scientist Joseph Highland said, "If I were a parent who observed the ceiling flaking, I would keep my children out of school."