On getting used to family life. Harness-chafings of a 30-ish couple

thirtysomething ABC, tonight, 10-11. Premi`ere of new dramatic series. It's a moment of transcendent joy as Michael and Hope gaze on their baby in her tub. She seems to shine in their eyes.

But then there's also the time Hope is at a restaurant with an unmarried friend, a snappy career woman. Would you believe it, she asks Hope - she now has 27 people under her! Hope not only believes it; she writhes inwardly.

Two scenes, two attitudes, two sides of the pyschic struggle depicted in this sometimes penetrating look at the intermixed lives of a young, yuppie-ish married couple and their friends. Through them - and despite a self-conscious introspection that is sometimes tedious and overwrought - this show brings something unusual to a prime-time series: a serious grappling - less formula-ridden and quite cinematic in feel - with the personal, family, and work needs of a certain generation of Americans.

Although the tough, explicit dialogue and scenes require parental discretion even at this relatively late time slot, the ending finds the couple opting for a moral and responsible course that reinforces family values while facing today's economic and social realities.

But it's after lots of anguish and torn feelings. After Hope and Michael meet and marry and Janey is born, you can almost hear those words from the old song: ``Those wedding bells are breaking up that old gang of mine.'' Dark, smoky scenes reflect the couple's pressing doubts. Other episodes record the penalties their family commitment seems to impose. Hope's restaurant scene, for instance, is a cutting picture of the havoc created by Janey, whose crying shatters Hope's attempt at a meeting of minds with her friend and reinforces her doubts about motherhood.

And there's the ad agency Michael and a colleague have formed - it's a struggle. We also see Michael at home amid breakfast chaos that signifies the mental mess their new life has made. Another time, clutching wistfully at his former free life style, Michael wants to go backpacking with another couple. A baby sitter is needed, but the candidates include the dropper (who says it's OK if babies fall because they have rubbery bones), the Nazi (crying is good for their lungs), and the vamp (a husband threat). Hope gives it up in a tearful, despairing recognition of how much her baby depends on her and how clean a break from her old life it is going to require.

This is part of what TV should be trying to do - to bounce visions of the viewers' social environment off their consciousness, to hold the mirror up to segments of modern society. Even if it is derivative of certain kinds of films, and tends to keep re-singing the song of lost freedom, ``thirtysomething'' is at least willing to enter this tricky milieu on a weekly basis.