"Imagine," says the letter from Fairfax Republican Del. John S. Buckley. "The Department of Education could force your child or grandchild to sit in a classroom and hear that homosexuality is natural and decent."

The letter, signed by the 27-year-old Northern Virginia conservative, has been mailed to about 20,000 people in the last two months, seeking contributions for an Arlington think tank to combat "militant homosexuals, free love advocates, radical women-libbers and pornography merchants" by abolishing the federal education agency.

Buckley, a cousin of conservative columnist William F. Buckley Jr. and a Washington political consultant, charges in the four-page letter that the Department of Education should be dismantled because it is "fueled by ultra-liberal, special-interest money, militant homosexuals and 'sex educator counsellors.'"

Federal education officials blasted Buckley's direct mail campaign as "ridiculous, absurd and false."

"There's a lot of misinformation in that letter," said Lou Mathis, an acting assistant secretary of education.

Buckley, who won election to the Virginia House of Delegates through a direct mail campaign of his own, said in an interview that he authorized the mailing under his General Assembly letterhead and defended his action. He rejected charges that the letter contains falsehoods, although he acknowledged that he did not know the source of any of the specific allegations it contained.

He said he relied on his friends, Ronald W. Pearson, president of Public Advocate, the group which sponsored the mailing, and Eugene Delgaudio, the group's executive director. "These folks [Pearson and Delgaudio] wanted to send out the letter this way," Buckley said.

"They assured me the facts were documented, and I said, 'Okay by me.' This is not something I initiated."

The letter also drew fire from teachers' organizations as propaganda designed to draw contributions through appeals to fear and hatred.

"I didn't see anything in the whole thing that I thought was true," said Willard McGuire, president of the 1.7-million-member National Education Association. "They made it [the department] sound like a porno factory."

But if some of the people who didn't know Buckley -- the youngest member of the Virginia legislature -- were surprised, some who served with him in Richmond weren't. "I knew John Buckley was conservative, but I didn't know he was an idiot," said Del. Warren Stambaugh (D-Arlington). "I've got to believe that a 3-year-old on his staff wrote it for him."

A senior Northern Virginia Republican, who asked not to be named, said he believed Buckley's letter was ill-advised and off base. "What he did was unnecessary and did not reflect well on him, or his party, or the cause he was espousing."

Buckley, who is expected to formally announce that he will seek a second term in the assembly, was unmoved by his critics. "The facts of the letter are documented facts," he said. "If they don't like the tone of the letter, that's their problem."

"This is a cause I agree with," he said. "I certainly believe we should diminish the role of government in education."

The Education Department's Mathis denied claims contained in the letter that the department requires all children 9 years old to submit to "graphic and detailed sex education," that it requires public school classes on the benefits of homosexuality, and that it has mandated a "massive national sex education program" for all students.

"Everyone here is stunned by the nature of it," he said.

According to Pearson, the letter has drawn $30,000 to $40,000 in contributions to Public Advocate, a five-person organization that performs research on conservative topics, and several hundred thousand signatures on petitions seeking the dissolution of the federal agency. It was created by President Carter but Ronald Reagan repeatedly called for reducing its role during his campaign.

Pearson, who last year paid Buckley $100 for his help on a research project, also serves as vice president of Phillips Publishing Inc. of Bethesda, where he is managing editor of an anticommunist newsletter called the "Pink Street on the Left."

Buckley, a former national president of the Young Americans for Freedom, is regarded as one of the most conservative members of the Virginia legislature, where his major bill this past year was a measure he called a "truth in taxation" law that would have forced localities to give the public more information about proposed property tax increases.