With all the frenzy over the Internet, entrepreneurs have been able to create and sell companies for huge sums without ever earning a dime. But in what may be a record of financial weightlessness, America Online said yesterday that it would pay at least $287 million for a company that has never taken in a penny in revenue and has no plans to start charging money.

What the company, an Israeli concern called Mirabilis Ltd., does have is users, 12 million of them who spend an average of more than an hour a day on its Internet chat service. Ultimately, America Online hopes to put advertising on the chat service and sell its members products and services. ''When you talk about making money on the Internet, no one is doing more than America Online,'' said Robert W. Pittman, the company's president.

He compared the Internet today to the early days of cable television. MTV, which Mr. Pittman helped start, took in only $500,000 in revenue its first year.

Mirabilis is highly regarded among savvy Internet users for its chat service, known as ICQ (shorthand for ''I seek you''), which enables them to detect when fellow users are on line and to communicate instantly with them. With no promotion other than word of mouth, it has already achieved something of a cult status, growing at more than 50,000 subscribers a day.