Summer's ending, and two teenagers decide to kill themselves. "Surviving," the ABC Sunday night movie, at 8 on Channel 7, is the season's third network drama about adolescent suicide and, at three hours, the longest. Of that three hours, roughly 90 minutes is either pure crying or crying interspersed with shouting.

Grief is a very difficult emotion to portray credibly on the screen, any screen, and there are too many times when "Surviving" taxes one's concern rather than provoking it. In addition, the mothers of the two dead kids are played by actresses who have made such a specialty of unraveling and imploding before the cameras that they give the film a distinctly recycled air. It begins to seem less the portrait of trauma it was meant to be than merely the latest misadventures to befall Ellen Burstyn and Marsha Mason.

Burstyn does have good moments, angrily and ferociously good, as the mother of a teen-age boy whose anguish she is too fashionably busy -- with visiting foreign exchange students and her attempts to master Chopin on the piano -- to notice. Len Cariou contributes a rather distracted performance as her husband, a wealthy doctor who's been having an affair. The son's discovery of his once-idolized father's culpability triggers (not completely believably) the suicidal impulses.

Meanwhile, the daughter of family friends has returned home after an unsuccessful wrist-slashing episode. When the boy and girl get together, they magnify each other's despair and, because their families fail to recognize the danger signals, something horrible occurs behind the tightly closed door of a garage. While at the Cariou-Burstyn household the father is most clearly to blame, it's the mother played by Mason who is the more thoughtless and callous of the married friends. Her husband is a weak-willed toady played toadyingly by Paul Sorvino.

In a way, the movie falls to pieces when the parents go to pieces, following the discovery of the bodies. For one thing, this marks the disappearance from the film of Molly Ringwald, the beguiling and thoughtful actress who plays the doomed young woman. Ringwald, who starred in "Sixteen Candles" and appears in the current "The Breakfast Club," is one of the most promising and casually scintillating young actresses around. Her freshness is a contrast here to the slightly stale professional slickness of Mason and Burstyn. The teen-age boy is played by Zach Galligan (of "Gremlins"), an inhibited and self-conscious youngster who is completely outclassed by Ringwald.

With each succeeding teen-age suicide movie, the parents involved seem to get more affluent. At the current rate of inflation, the next one will have to be about teen-age suicide among the Ewings and the Carringtons. Perhaps writer Joyce Eliason thought that making both families so outrageously comfortable would add to the pungency and irony of the teen-agers' dissatisfaction. But the movie, after all, is called "Surviving," and it asks us to care a great deal about the surviving parents. We don't. They seem silly, shallow people who have garden parties around their swimming pools, drive Jaguars and live in semipalatial California splendor. Is the average viewer supposed to identify with these wealthy folk, or are we to think that domestic trauma is tougher on the rich than the poor? I wouldn't hold my breath waiting for a TV movie about an inner-city teen-ager who takes his own life out of hopelessness over poverty and his abandonment by society.

Eliason hands most of the required public-service information about telltale signs of excessively depressed young people to a doctor played by William Windom. He recites some of them at the youngsters' double funeral. The sad national statistics about teen-age suicide soon follow. You wouldn't be surprised to hear Burstyn exclaim something like, "Oh, I feel just like a character in one of those noble TV movies!"

Obviously a film like this has basic instructional duties to perform, and it performs them. It can't be judged solely as drama because, like many TV movies, it has taken on an additional utilitarian, pro-social chore. If a viewer is not convinced of the veracity of the narrative, however, and finds the characters transparent, the sermonizing may have little practical effect. On the other hand, director Waris Hussein has seen to it that audiences desirous merely of another exhausting tear-jerker will certainly be all sniffled out by the time "Surviving" ends on -- as one might expect -- a tiny note of hope.