But excuse me for thinking that E-mail had already licked the problem of how to talk to one another on line. No one is more excited than I am about the Net, the most revolutionary communications medium of the century. Intrigued, I went to the Mirabilis site (From all appearances, the main thing it offered was the opportunity to download yet another free software tool that promised to let me communicate with other people on line. ICQ is reported to be the most popular Internet software downloaded from the Net. ''We're not really sure how to characterize it,'' agreed Doug McFarland, senior vice president of Media Metrix, which ranked Mirabilis 29th in March among the 5,300 sites home users visit most frequently. Instead, Mirabilis is a software company, based in Tel Aviv, whose main product is a free chat and messaging program called ICQ (pronounced I Seek You). Nor does it run banner advertisements on other sites.

It isn't a search engine, after all, or a place where I can go to download a browser or the on-line headquarters for some mammoth on-line service. That was certainly curious news because Mirabilis does not fit my idea of the kind of site that should be wildly popular.

In April, Mirabilis had more than two million visitors. THE other day, as I was scrolling down a ranking of the most popular Web sites, I found myself stifling a yawn as I was confronted with the usual suspects: Yahoo (been there), Netscape (done that), America Online (ho-hum), Microsoft, Lycos, Excite (yeah, whatever), Mirabilis.

Icq new user