XM Satellite Radio threw its latest punch today in its ongoing scrap with Sirius Satellite Radio, unveiling a pair of portable, handheld radio receivers that will also store downloaded music.

The two devices, called the Helix and the Inno, are manufactured by Samsung Electronics and Pioneer Electronics, respectively. As part of XM's XM2Go line, each device lets users bookmark songs while listening to XM's 160 channels of programming and download songs online through XM+Napster, the company's joint venture service with music-download service Napster. Each will sell for $399.99 in the first quarter of this year.

"When you combine live XM Radio with a portable MP3 player that lets you buy songs you hear on XM from Napster, you have a 360-degree music experience," XM chief executive Hugh Panero said in a statement. "Now you can get the best of both worlds in a single device that fits in the palm of your hand."

The devices are about four inches tall, two inches wide and one inch thick, weighing 4.5 ounces each.

Both devices are "fully capable" XM receivers, meaning they can play in the home or the car. An integrated wireless transmitter allows users to play live XM content through any FM radio, whether in the car or in the home.

Both the Helix and the Inno have flash memory that allow for storage of up to 50 hours of XM programming. Both will be able to play MP3 and Windows Media files, the latter of which is the format used by Napster. The XM+Napster service costs $9.95 per month.

The move comes as the fight between XM and Sirius is heating up amidst a host of other competitors from outside the satellite radio space. Sirius already introduced its own line of hybrid audio players last August, the S50, which attaches to a docking system in a car, home, or office to receive content but is also portable.

The companies have been engaged in a celebrity tête-à-tête of sorts, with XM hoping to answer Howard Stern's much-hyped January 9 arrival on Sirius with celebrity signings of its own, including Bob Dylan and Snoop Dogg.

Sirius has long played second fiddle in the space, counting barely one million subscribers to XM's five million in the middle of last year. But Sirius said last week that the anticipated subscriber surge from Stern's arrival has already happened, pushing the company over the three million subscriber mark.

Meanwhile, cell phone maker Motorola revealed details yesterday of iRadio, the subscription radio service it plans to launch later this year. The service will include 435 commercial-free radio channels through Clear Channel Radio, including such niche stations as "Rockin' Cowboys" and "Angry Women." It will be available on Motorola's Rokr E2 phone, the first incarnation of which featured Apple's iTunes.

That's not to mention the zillion-pound gorilla in the portable music space, Apple's iPod, and plans by mobile service providers Cingular Wireless, Verizon Wireless, and Sprint Nextel to roll out their own wireless music download services.

XM also unveiled a line of Samsung MP3 players that only receive XM Radio reception when connected to a home docking station or car dock. The Samsung Nexus players store 25 and 50 hours of programming, respectively, and cost $199.99 and $249.99. Both players will also let users bookmark songs to buy through XM+Napster.