THERE was a time not so long ago when the Manhattan Eye, Ear and Throat Hospital on East 64th Street was as chic a destination for Christmas vacation as St. Barts or Telluride.

That is where many teen-aged girls would disappear during school holidays to get the ethnic bumps on their noses smoothed out. So crowded were the operating rooms at this time of year, recalled Dr. Gerald H. Pitman, a plastic surgeon, that he would set out 20 sets of rhinoplasty instruments in the morning and run out before the day was done.

But the crowd is thinning.

In the midst of an explosion in cosmetic surgery, the number of nose jobs has dropped significantly. While the total number of cosmetic procedures increased 76 percent, to 697,000 from 395,000, between 1992 and 1996, the numbers of rhinoplasties, as they are known, fell 8 percent, to 46,000 from 50,000. And the decline was probably steeper between the 1990's and the 1970's, experts say, although no statistics are available before this decade.

The reasons are partly cultural and partly economic, according to plastic surgeons who have watched the evolution of a procedure that was once a benchmark in a young girl's life, especially among Jewish teen-agers.. ''It was the thing to do,'' said Dr. H George Brennan, who practices in Southern California. ''You had your bat mitzvah and you got your nose done.''