NEW YORK - Area code 212's number is up. And that means New York could become the nation's first city with three area codes.

With the proliferation of faxes and computers using phone lines, New York Telephone expects to run out of numbers for that area code in Manhattan and the Bronx in 1993, company spokesman Peter Muller said. The company has already reserved 917 for future use.

The state Public Service Commission in Albany has voted to begin looking at the issue and to solicit comments.

One option would be to assign the new area code to cellular and pager numbers, said commission spokesman Edward Collins. No area in the country has a special area code for portable phones and beepers, he said.

The five boroughs that make up New York City used to have one area code: 212. In 1985, the numbers in that area code were used up, and the 718 area code was created for Brooklyn, Staten Island and Queens.

New York and Los Angeles are the nation's only two cities with two area codes.