This double debut of two young abstract painters indicates that the impulse to build on 1960's-style abstraction has both possibilities and pitfalls. Tim Bavington's elongated canvases covered with blurry but tightly vertical stripes suffer from familiarity. The color changes are beautiful and the stripes are sometimes highlighted in ways that have an animated optical effect. But in terms of technique and concept, and except for the narrow line of grisaille stripes along the bottom edge of ''Before Today,'' these paintings look as if they could easily have been painted in the 1960's. In particular, they suggest Gene Davis's stripe paintings as rendered by Dan Christensen in his paint-can days.