While DirecTV and Comcast slug it out for high-definition supremacy, a couple of big telephone companies are trying to take small slices of market share from the U.S. satellite and cable television leaders.

Last week, both Verizon’s FiOS and AT&T’s U-verse fiber-optic television units announced improvements to their high-definition programming inventory.

AT&T said U-verse, with the addition of three HBO channels, has more than 40 regularly programmed HD channels, while Verizon said FiOS will have more than 1,000 video-on-demand titles by the end of the year.

Both companies say their fiber-optic television services will have 100 regular HD channels by 2009.

FiOS, started in September 2005, had a nine-month head-start on U-verse, although the services don’t directly compete because of AT&T and Verizon’s regional exclusivity.

Still, executives with both companies are touting fiber optic’s quality over DirecTV and Comcast’s quantity of HD content.

“We’ve got more HD linear channels than our cable competitors, and more attractive content choices than any of our competitors,” said Dan York, executive vice president of content and programming at AT&T. He added that because data transmitted through U-verse uses Internet Protocol, the video and audio quality of its broadcasts is superior.

Verizon yesterday sued Time Warner Cable, saying the No. 2 cable operator's advertisements are false because they claim that FiOS requires its customers to get a satellite dish, and that FiOS is an inferior product to Time Warner Cable service, Reuters reported. A TWC spokesman said the suit was without merit, according to the wire service.

Verizon and AT&T aren’t exactly Davids to DirecTV and Comcast’s Goliaths, as the telephone companies’ combined market value of about $340 billion is triple the $92 billion combined market value of the satellite and cable leaders. Still, the combined subscriber total for U-verse and FiOS at the end of last year was about 1.2 million, compared to about 24 million for Comcast and 17 million for DirecTV.

Such dominance may gradually wane as more customers looking to bundle television service with Internet and telephone services gravitate toward FiOS and U-verse. While cable companies’ market share is expected to fall during the next decade and satellite TV demand to remain flat, telecommunications companies, whose market share was negligible last year, will account for about 11% of the market by 2017, according to research firm SNL Kagan.