But a year later, Mr. O'Brien is still here, continuing to occupy the 12:35 A.M. slot on NBC five nights a week. How has he defied the odds thus far? A good share of the credit goes to his young, overworked writing staff, which dreams up three or four offbeat comedy sketches like the "Hee Haw" parody each day. It is, as even Mr. Letterman has remarked, the writers who have set Mr. O'Brien's show apart from the parade of other talk shows that clog the dial.

"The more I watch the show, I realize you guys do an incredible amount of comedy, and stuff that is produced, that is very high level," Mr. Letterman told a beaming Mr. O'Brien in February during a guest appearance on "Late Night." "And the volume and quality of the stuff just knocks me out."

To be sure, other forces have conspired to keep the 31-year-old Mr. O'Brien on the air. Up until now, he has had little real competition in his time slot. That will change dramatically this winter, when Tom Snyder returns to late-night television with a one-hour talk show following Mr. Letterman's wildly popular "Late Show."

Still, if Mr. O'Brien has proved anything over the last year, it is that his appeal should not be underestimated. Fidgety and visibly uncomfortable during his initial outings last September, he has begun to settle into a more confident, self-deprecating persona that is equal parts silly and quick-witted. And although they have a way to go, Mr. O'Brien and his sidekick, Andy Richter, 27, have begun to develop a dry, buddy-buddy banter that at least some viewers seem to be warming to.

"Late Night" 's ratings have shown noticeable improvement. In July and August, the show averaged a respectable 2.0 rating, up about 11 percent from the 1.8 average rating in its first six months on the air. (Each ratings point represents 942,000 households.) Many of Mr. O'Brien's viewers are college students, who spike up the ratings significantly when they are home on vacation, since Nielsen ratings do not measure viewership in college dorms.