Jean's letter begins: "Dear Darling - just want to tell you that I do love you." She goes on to propose trysts "whenever it is possible," predicts the result would be "the most handsome son you have ever seen," and ends, Darling, please answer my letter."

He never will. He's never heard of her. Besides, he's an associate justice of the Supreme Court of the United Sates.

"Jean" can't be identified. She hadn't bothered to give her last name.

The source of this unusual tidhit of news also can't be identified, because the justice and I struck a bargain: in exchange for a rare opportunity to examine the mail received by a member of the court, I would identify neither him nor the letter writers.

To keep his part of the bargain, the justice directed his staff to screen our personal and official mail and after examining all unsolicited communications, to save them in a box in the closet. Generally, members of the court, who have tiny staffs, don't answer unsolicited letters and postcards from the public.

This continued for about six weeks, until anyone who wanted to comment on the court's crucial end-of-the-term decisions had ample time to do so. Then a clerk delivered the letters - including Jean's - to the reporter.

The letters and cards totaled 95. A tiny number? Yes, alongside the avalanches of mail - wanted, unwanted and heavily orchestrated by interest groups - that come to presidents and legislators.

But, unlike elective officials, justices are lifetime appointees. They have no constituents to please or serve. They ask no one to write to them. To do so would conflict with their mission to be guided not by popularity or public opinion, but by the Constitution and the law.

Actually, even the figure of 95 is deceptively high, because the number of writers was only 81. One of them sent seven letters. Each consisted of a notarized statement of his views of the Constitution followed by an accusation that various persons were violating it, and a copy of a column that appeared on May 25 in Newsday. The writer never said what his point was.

Pewer than half of the letters and cards were typed and the typing frequently was messy: of the 55 that were handwritten, many were scrawled out to all four margins or if legible, were incoherent.

Some correspondents uncluded the justice among perhaps a dozen scattershot addresses, including President Carter, legislators, other members of the court, and reporters.Much of the subject matter was unrelated to the business of the court, ranging from theories about assassinations to cures for global water shortages to the nuisances of barking dogs in campgrounds and of marijuana smoking on intercity buses.

A couple of correspondents were adulatory. Writing on the Fourth of July, a Florida man said that Americans owe the justice "a fervent debt of gratitude" for consistently "Solomonlike" and "gracefully literate" decisions.

More correspondents were abusive, relentlessly stringing out unprintable words to denounce various persons or institutions or religious faiths.

In the Allan Bakke case, the justice was one of the four members of the court who would have upheld the affirmative action plan with which a medical school set aside 16 of 100 admission slots for racial minorities.

"You should be ashamed of your miserable self," wrote an Orange, Calif. man. "Do you have the slightest idea of what the U.S. Constitution is all about?"

"Your sir," said a Reno, Nev., man, "are a lousy Supreme Court justice. YOUR MIND IS CLUTTERED WITH CLAPTRAP."

"May poor health and misfortune follow you until you see the error of that decision," wrote a retired military man 57 years old."

Another correspondent denounced the justice's "insane ruling," although the ruling was not his, and demanded his resignation.

Yet another, "Tired of your group of legal clods," wrote "The next lawyer or judge I meet will have his face punched in."

"Sincerely . . ."

The justice was also the recipient of a letter from a New York City man who denounced the entire court for "a right result, but a damned lousy decision," and who attacked the second bloc of four justices - those who wanted Bakke admitted without reaching the issue of affirmative action - as "four moral cowards."

One correspondent, a firm but not vituperative professor of social science in Michigan, told the justice, "You are institutionalizing racial inequality," despite the command of equalty in the Constitution.

In all, the justice got a dozen letters on the Bakke case. Not one endorsed the position he took.

After deciding Bakke, the court, without comment or disclosure of the vote, let stand a ruling upholding the far-reaching affirmative action plan in effect in the Bell System. This prompted a letter from the president of a local of the Communications Workers of America (AFL-CIO), which had challenged the plan.

The union official expressed "deep disappointment" and detailed his reasons ("We have had black members discriminated against, we have had females discriminated against . . . my members have to pay the price of [AT&TS] discrimination; this is not what I believe to be justice under our Constitution.

The tone of the letter was respectful throughout. "I probably have no right to ask you to reconsider . . . but I feel very deeply that I must." the local president wrote.

The only letter from a person who is, or who said he is, a lawyer, was complimentary. The stimulus was the decision in the "duty words case," in which a divided court upheld the power of the Federal Communications Commission to reprimand a radio station for having broadcast seven words describing sexual and excretory organs and functions.

Complimenting the dissenters, who included the justices, the lawyer wrote, "It is not for the Supreme Court . . . to dictate what is good or bad for me or anyone else . . .."

But the six other letters on the case were critial."A nation against God is a nation against itself," said an Arkansas woman. A New York City woman faulted the justice's lack of "orderly thought."

Two Minneapolis couples signed a letter saying, "Given a chance, we would vote you out so fast, but we've stuck with you for life ." A Berkeley, Calif., man, drawing on a traumatic childhood experience, warned that certain "dirty" words can have harmful effects when spoken in the presence of "ultra-sensitive pregnant women."

Although it's 5 1/2 years since the court's abortion decision, two Syracuse women, apparently sisters wrote seven separate cards in four weeks urging the justice to reconsider the vote he'd cast with the majority so as to "stop the bloody murder." Similarly, a Newark, N.J. man wrote twice in 10 days to say that "Gods's command should induce you to seek reversal," adding "I have you in my prayers."