IT IS FITTING, I think, that a year that began with Shelia Rabb Weidenfeld's memoir of her months as Betty Ford's press secretary, First Lady's Lady , should end with a novel by her archenemy, Ron Nessen. There is a pleasing symmetry in this, an elegant balance. There is also in these two books' a final vindication of the keen political insight of Chevy Chase and his former colleagues on "Saturday Night Live." Here, the gentle reader will find ultimate proof that any American citizen over the age of 35 really can become president.

I am assured by no less a figure than James A. Michener that Nessen's The First Lady is a roman a clef; a letter to that effect is reporduced on the dust jacket. So be it. Modeling his prose on that of Franklin W. Dixon, author of the Hardy Boys series, Nessen weaves a tangled skein of fate about the lives of Ted Blair, a former baseball player turned chief executive -- he appears to have been traded up, for there is no other possible explanation for his presence in the Oval Office -- and his beautiful but desgruntled wife, Libby. Enraged because the jackals of the press have accused her of using Air Force One for shopping trips and because her husband prefers the company of Yogi Berra, Libby seeks revenge by sleeping with her husband's military aide and by flying coach on a commercial airline. She ends up getting herself kidnapped by a crazy Puerto Rican, a psychotic black, a girl and a Japanese. The response of the president to this catastrophe is to sit around and try to think, like a character in a Thurber cartoon. The ambitious defense secretary, Harold Kaiser, immediately begins to plot -- which is more than can be said for the author -- and the presidential press secretary makes a lot of dumb mistakes. There is a happy ending.