Absence makes the heart grow fonder; but out of sight, out of mind. Or so goes one of Norman Luboff's paradoxical, pithy paraphrases for unaccompanied choir called "The Proverbial Contradictions of Life," sung last night at the Terrace Theatre by Paul Hill's Washington Singers. It is a surprisingly good series of very short jingles, no more than a few bars each, void of pretensions and full of melodic good humor. And as with the rest of the program, guest conductor Luboff led the group with crispness and grace.

Samuel Barber's "Reincarnations," Op. 16, brought out the best singing with newly found strength in the tenor sections. If the sopranos had pitch problems there as well as in four acapella songs by Brahms, the overall vocal fabric was smooth and colorful.

Singing soft can be hard, and the Washington Singers could do some work in this area. In Brahms' "Waldesnacht," one would have enjoyed the variety and pleasures that come from hearing pianissimo singing, and a group this small should be able to produce occasionally softer, finely focused sounds.

The concert, billed as "Music of Love and Romance," also included several other works by Luboff, and some delightful Moravian Duets by Dvorak.