Sirius Satellite Radio Inc., the No. 2 U.S. pay-radio company, will begin selling its first portable device to compete with larger rival XM Satellite Radio Holdings Inc. and products such as the iPod.

The Sirius S50, which will be available for $359.99 in October, will store and play back as much as 50 hours of radio, New York-based Sirius said yesterday in a statement. The device, about the size of a deck of cards, can be strapped on an arm or clipped to a belt.

The product may help Sirius catch up to District-based XM, which already has a portable player on the market. The two companies are trying to win subscribers to their pay services by striking deals with car makers to include their receivers. They are also targeting fans of music downloading who buy the Apple Computer Inc.'s iPod, the top-selling U.S. player.

"Sirius is moving in the right direction," said April Horace, a Denver-based analyst at Hoefer & Arnett Inc. who rates the shares "buy" and said she doesn't own them. "Sirius has historically been behind XM as it relates to technology."

The companies are also seeking subscribers by signing up star hosts, including Howard Stern and Martha Stewart at Sirius and Bob Edwards and comedians Opie and Anthony at XM.

The Sirius S50 includes the portable player and a home docking system that has the satellite receiver. It has a 1 gigabyte flash storage. The device must be attached to a home or car system or computer for downloads.

Sirius isn't selling a portable receiver because satellite signals get blocked by buildings and bodies, spokesman Jim Collins said.

XM Satellite sells several portable receivers including the MyFi, which costs $299.99 and measures 4.5 inches by 2.8 inches by 1.2 inches deep.

Sirius programming costs $12.95 a month for more than 55 channels, the company said.