In tradition and in poetry, the marriage bed is a place of unity and harmony. The partners each bring to it unselfish love, and each takes away an equal share of pleasure and joy.

At its most ecstatic moments, husband and wife are elevated far above worldly cares. Everything else is closed away.

This is the ideal. But marriage experts say that such mutual contribution and mutual joy are seldom achieved. Instead one partner or the other dominates the sexual relationship. In the past, it has been the husband who has been dominant and the wife passive. But today there are signs that these roles are being reversed.

In a growing number of American homes, marriage counselors report, the wife is taking a commanding role in sexual relationships. It is she who decides the time, the place, the surroundings, and the frequency of the sexual act. It is she who says aye or nay to the intimate questions of sexual technique and mechanics -- not the husband. The whole act is tailored to her pleasure, and not to theirs.

Beyond a certain point, of course, no woman can be dominant -- nature has seen to that. But there is little doubt that in many marriages the wife is boss of the marital bed.

Of course, there remain many ``old-fashioned'' marriages in which the husband maintains his supremacy. Yet even in these marriages, psychologists say, wives are asserting themselves more strongly. The meekest, most submissive wife of today is a tiger by her mother's or grandmother's standards.