Congressional librarian David Mearns' portrait of Lincoln is achieved through a collection of random pieces pertaining to or influenced by the personal life of the great president. Written with zest, witty and urbane, this should titillate the scholar, amuse the social historian and provide good browsing grounds for the budding biographer. However the average Lincoln fan had better dust off his Sandburg-- the debonair approach here is not for the log cabin devotee. At any rate, running through a great deal of material, hard-to-come-by letters, senatorial gossip, household data, newspaper clippings, sharp profiles of ambiguous Secretary Stanton, bombastic Judge Douglas, romantic Mr. Booth, along with the various predilections, eccentricities and colloquialisms of the fabulous Abe, what we get is one of the least rustic versions of the man. It is admittedly marginalia, garlanded with conjecture, but provides a new approach to an inexhaustible subject.