REDWOOD CITY, Calif. (AP) _ At Home Corp. announced today that it will form a joint venture to bring its high-speed cable Internet-access service to 5 million homes in Japan.

The venture, called At Home Japan, will also be partly owned by Japanese cable operator Jupiter Telecommunications and one of that company's owners, trading giant Sumitomo Corp.

``With roughly 15 million Internet users, Japan is an extremely promising market for high-speed cable Internet services and a tremendous next step in At Home's international expansion,'' John O'Farrell, senior vice president of international operations for At Home, said in a statement.

At Home will own 43 percent of the venture, Jupiter Telecommunications will hold 36 percent and Sumitomo will own a 21 percent stake, O'Farrell said.

At Home now has about 330,000 customers in the United States and Canada who use its high-speed Internet access. But it has partnerships with 21 cable operators that give it exclusive access to sell to about 60 million homes. Analysts expect At Home to have 1 million subscribers by the end of the year.

At Home plans to launch a service in the Netherlands this fall aimed at 1.4 million users. That venture is co-owned by At Home, Dutch cable operators and Intel Corp.

About 11 percent of Japanese households had access to the Internet at the end of March, nearly double the amount of a year ago, according to Japan's Ministry of Posts and Telecommunications.

Jupiter Telecommunications, founded in 1995, is a joint venture between Sumitomo and Liberty Media International Inc. Liberty is part of a spinoff of Tele-Communications Inc., which was recently purchased by AT&T Corp. AT&T holds a controlling stake in At Home.

Jupiter Telecommunications provides cable TV to 348,000 homes in Japan. Its franchise, including Sumitomo's cable systems, covers 5.1 million homes in 29 cable systems.