In the old days when a senator practically could appoint any postmaster in his state, one solon acknowledged that the power was not an unmixed blessing. "You make one friend, and the other nine disappointed candidates become your enemies," he pointed out. There are days when reader complaints paint a similar picture -- many letters to the editor are written, but relatively few are published, and to judge by my mail, disappointment is heavy.

The problem is that The Post's editorial department receives 50,000 letters a year and there is space for less than 10 percent of them, even with an extra full page of letters Saturdays, more space than most papers provide.

Letters to the editor inevitably rate high in readership surveys, and competition to get into the columns is heavy. Motives vary: some take pen in hand because they don't like the way the world is going; others take exception to a Post report or commentary; some try to get coverage for an event; some to show association membership that they are on top of events and making their voice heard; and some, I suspect, just enjoy seeing their name in print. In addition, there are a few elitists who believe they are entitled to a half-column almost every week.

Some letters have kicked off lively exchanges. One was over Welsh "rabbit" versus Welsh "rarebit." That began in 1982, hopped into 1983 and led to a pamphlet including this editor's note: "Hare today, gone tomorrow. This correspondence is closed." But no, a week later came a final word from a member of Britain's Parliament.

A more recent letters fuss was over Nestoring -- John Nestor's practice on the Beltway of holding the passing lane at the legal limit of 55 mph despite the cars and rucks that value speed over obedience. (There must be some subtle commentary here about what really turns readers on.)

The editor of the editorial page, Meg Greenfield, is enthusiastic about the letters column and said she was in "continuing lament" for space to permit more than the average 80 letters a week. Right now, "first consideration is given to people or institutions that have been written about and believe themselves to be badly dealt with." William McPherson, editorial writer and columnist, is responsible for selecting letters.

Another way to take exception to Post coverage is to submit an article for the opposite editorial page. But here, too, 600 to 700 unsolicited manuscripts are received a month.

A second priority for publishing letters goes to "general reader observations about material in the paper or missing from the paper. Local or community issues take higher precedence than national or world matters," Miss Greenfield said.

Some warnings: "No anonymous letters. Regulars are discouraged -- it is not fair if they get all theirs in. We are also terribly leery of fund-raisers or crowd-gatherers. We are not a billboard for good causes," she noted.

How do you improve on the 1-in-10 odds? Miss Greenfield suggests, "Be relatively brief, be timely and write about something that has been in the paper." And if it doesn't get published, try again.

Why not a letters column on television news programs? Several months ago, Bill Monroe of NBC News reported "the virtual absence of a legitimate letters mechanism among television stations and networks." At the time, Monroe noted, there was only about a minute of excerpts from viewers' letters on the CBS "60 Minutes" program, and his own show, "Meet the Press," then occasionally carried a few excerpts, too.

Now Mr. Monroe is experimenting with a segment of viewer reaction for the NBC "Today" show. From about 100 letters a week, two or three "well phrased" ones are selected and the authors filmed at their homes.

A recent "Today" piece dealt with some television stations' acceptance of contraceptives advertising. An NBC official was against it and a family- planning expert for it. Letters reacting ran about 2 or 3 to 1 for the ads, with "one writer arguing that since TV encourages people to be interested in sex, it ought also to let youngsters know how they can protect themselves," Monroe reported. The letter- writers were seen on a four-minute segment prepared by Monroe.

It isn't 80 letters a week, but it's a start.