The "Watergate babies," the 86 House members who came to Congress in 1975 determined to change the world, seem to be dropping out in middle age. Only 16 returned to the House this Congress, and of them, two have resigned and four others have announced that they won't run again next fall. By comparison, none of the 13 surviving members of the class of 1972 has announced retirement. The class of 1974 hit the House like a hurricane, setting off a revolt that toppled committee chairmen and forced rules changes weakening the power of the leadership. But the intervening years have been frustrating. Despite the early promise, only one Watergate baby, Interior Committee Chairman George Miller (D-Calif.), has become chairman of a standing committee.