April is the cruelest month for the producers, writers and actors who have prepared pilots for the scrutiny and judgment of network executives putting together their fall schedules.

Months, even years, of development can go down the drain within an hour if the executives rise from their seats in the screening rooms and signal, as did the ancient rulers of Rome, thumbs down.

Though television is little more than a quarter of a century old, these annual rites of spring have become a deeply entrenched tradition in the business. It's a sorting out that leaves hearts broken and coffers emptied.

But this spring offers two noteworthy departures from established tradition, a breaking out of the pattern whereby producers are left to the not-so-tender mercies of a three-network market.

They are the new Norman Lear series on male-female role reversal, "All That Glitters," which starts this week on about 45 individual stations, and MCA TV/Universal's adaptation of Taylor Caldwell's "Testimony of Two Men" on about 90 stations.

The latter is a limited mini-series. "All That Glitters" is an effort to duplicate Lear's success with "Mary Hartman, Mary Hartman" by producing five 90-minute episodes a week. Whether the shows succeed, people in the television industry will be watching closely to see if there is a fourth market outside the three major networks.

There was a brief flurry of attention several months ago at an announcement by Metromedia Television and the advertising agency of Ogilvy and Mather about their joining to create what was called a fourth network. It now has turned out to be more flurry than substance.

There is a very simple reason --money. Few groupings in television can put together the money and the facilities that the three major networks provide to producers, writers and actors. In Hollywood today, only large and successful organizations like Lear's and MCA TV/Universal can challenge the dominance of ABC, CBS and NBC in the field of programming.

Lear's motivations and MCA TV/Universal's are the same: they want to make a buck. There is an added factor in Lear's thinking. He wants to use comedy to push back taboos that have limited television's willingness to offer viewers levels of maturity that they are seeing in movies or reading in books.

But breaking the three-market syndrome is still a major goal. Frank Price, the head of MCA TV/Universal, put it to me very succinctly during a recent visit to Hollywood. "We're very much in a three-buyer business, and any business is better if you have four buyers or five buyers. The idea of encouraging another buyer is ultimately beneficial."

This does not mean that Lear or Price want to see the networks broken up. Both producers are heavy suppliers to the networks. They are simply seeking a way to escape from the annual rites of spring, when their products are subject to the scheduling imperatives of three buyers.

Like most early stirrings of spring, "All That Glitters" and "Testimony of Two Men" are merely harbingers of blossoms rather than a full flowering. But my guess is that over the coming seasons, these seeds will grow.