HIGH-definition TV – the long-promised TV of the future – has quietly passed from “The Jetsons” into the mainstream in recent months, TV experts say.

This week alone some of the biggest shows on TV, including “CSI,” “ER,“ “West Wing” and “Law & Order” are all being broadcast in HD format. The Super Bowl will be in HD as will college basketball’s Final Four.

ABC is even planning to air this year’s State of the Union address in HD format.

“The shows that America watches are all in HD,” says CBS executive vice president Martin Franks.

“I remember when color first was introduced, and you scanned TV Guide looking for the shows that were in color,” he says. “There were one or two.

“That was the way it was with HD – for a while.”

Without much fanfare it seems, the most revolutionary change in TV since color was introduced in the early 1960s has become every day – if hardly yet in every home.

It is estimated that of the 105 million TV homes in the U.S., about 5.8 million have HDTV sets. The Consumer Electronic Association, an industry trade group, expects that number to grow to 16.2 million by 2008.

When HDTV was first introduced about five years ago, an HDTV set cost as much as $20,000. This year the average cost is about $2,000. By this time next year, they are expected to fetch less than $1,000.

Most plasma screen TVs – one of the hottest gift items from the past holiday season – are either HD ready or need a simple converter hooked up to become HD sets.

“But there’s a lot of people who aren’t looking to spend that kind of money on things like entertainment systems,” says Jupiter Research analyst, Michael Gartenberg. “Even when the concept becomes appealing, it’s easy for them to get totally lost in the buzzword and jargon of the industry and end up not making the purchase.”

For nearly a decade, broadcasters have been undergoing a wholesale conversion of the U.S. TV system to HDTV, heralded as a better way of sending and receiving pictures and sound.

So far, three of the four major broadcast networks – CBS, NBC and ABC – offer the bulk of their primetime scripted shows and major sporting events in HD format.

Fox is expected to roll out its HD schedule later this year.

Until recently, HD programming was limited, and signals could only be captured using a roof-top antenna, but that’s changed in most TV markets, especially New York.

HD broadcasts here can be received over the air, through satellite services like Direct TV and from two of the largest cable companies in the area, Time Warner and Cablevision.

Still, much of TV is not HD – and won’t be for some time.

Reality shows like “Survivor” and “The Simple Life” are not high definition because HD cameras are too expensive and too delicate for shooting in remote locations. For the same reason, news programming and none of the popular morning TV shows, like “Today,” are in HD.

The popularity of HDTVs is simple to understand: the picture is big and wide, razor-sharp and shaped more like a movie theater screen. The signal comes with CD-quality, five-channel surround sound and uses 10 times the number of pixels of today’s average TV viewing experience.

That means the picture is about five times sharper but is infused with more life-like color.

In an HD NFL telecast, you can see the pores on a player’s face, the texture of his uniform and the individual blades of grass that make up the field turf.

In a telecast from a rainforest the dew dripping off leaves looks real.

With the addition of a surround-sound system, the format transforms a scripted drama like “ER” or “CSI” into a theatrical experience.

HDTV Programming:

WHAT’S HDTV

Network

CBS – 100 percent of primetime

NBC – 95 percent of primetime

ABC – 100 percent of primetime

UPN – “Enterprise” “Jake 2.0” and select movie titles on Friday

WB – 70 percent of primetime

Cable: HBO, Showtime, Cinemax, Starz, Fox Sports Net, Thirteen (PBS), Bravo

WHAT’S NOT

HDTV Programming: No

Fox – Coming in 2004

News programming ranging from “Today” and “World News Tonight” to “60 Minutes”

Reality shows like “Survivor” and “Fear Factor”

Most soap operas

Dozens and dozens of cable channels