Just a month after stepping down from a top role at America Online Inc., Marc Andreessen is launching a start-up.

Andreessen, 28, a key figure in the establishment and growth of Netscape Communications Corp. in the mid-1990s, this week is unveiling Loudcloud Inc. The new company will provide software and services to other new technology ventures.

Loudcloud will be based in Menlo Park, Calif., but Andreessen, who owns homes in McLean and in Silicon Valley, said he would be doing some work in Northern Virginia.

After Netscape was bought by America Online, Andreessen became AOL's chief technology officer. Analysts said his role with AOL helped smooth the initial merger transition, but it soon became clear that Andreessen was more interested in nurturing companies at early stages. He began to invest in Silicon Valley Internet companies, such as Accompany Inc. and Replay Networks Inc.

Andreessen said he planned to continue funding other people's companies but felt a much stronger draw to starting his own venture. "I'm even more of an entrepreneur and less of a venture capitalist than I thought," he said.

Andreessen will be chairman of Loudcloud, which already has 20 employees, many of whom are former Netscape staffers.

Loudcloud is financed internally by Andreessen and other employees. His friend Ben Horowitz, who was at Netscape for several years before the merger and who last month also left his job at AOL, will be the chief executive.

Loudcloud's business will be to help develop new infrastructure for start-ups, Andreessen said, allowing new companies to contract out some of their technological needs by, for example, having their Internet operations hosted at Loudcloud data centers. He said the details of the company's offerings would likely be unveiled early next year.

"It's more of a technology company," Andreessen said. "We're not an incubator or venture firm."

As he launches this company, Andreessen is certainly looking back to the early days of Netscape, which he co-founded in 1994. But this time things are moving much faster, and he and his parters have more experience, he said.

"It's more fun this time because I have more of an idea what's going on," he said. "This time it's more exhilarating than terrifying."