LAS VEGAS (AP) _ Technology that would give Americans super-sharp TV pictures and CD-quality sound got rave reviews from broadcast engineers, but was called just an ``improvement'' over regular TV by a janitor who works at the convention center here where the first broadcast took place.

Using a special transmitter, CBS affiliate KLAS Monday broadcast in high definition, a digital format developed specifically for U.S. television. It was the first broadcast outside of lab testing.

``It's an improvement, but vast is too strong an adjective,'' said Daryl Allen, who works at the convention center. ``I was impressed _ as far as I can be by television.''

Broadcasters attending the National Association of Broadcasters annual convention here got to look at the super-sharp TV. KLAS viewers continued to get their regular programming in the existing analog format.

``I've been in broadcasting for 28 years and it just blew my socks off,'' said KLAS' chief engineer Jack Wilkinson.

The station's HDTV signal traveled unobstructed to the Las Vegas Convention Center, about half a mile away from the station. The signal was received on special equipment set up outside the center, routed to a makeshift theater inside and then to a projection TV with a rectangular screen.

``This provides broadcasters with an exciting yet realistic glimpse of what the future of over-the-air television will be,'' said NAB President Eddie Fritts.

Michael Jordan, chairman of CBS' parent Westinghouse Electric Corp. called the broadcast ``an important technical step and an important symbolic step'' toward making high definition a reality for TV viewers.

Jordan, NBC President Robert Wright and Fox TV owner Rupert Murdoch said broadcasters must go digital to be viable competitors in the 21st century. ``We just cannot let free over-the-air television become a second class medium,'' Murdoch said.

But the three executives have different views about the role of high definition television, which has even sharper pictures than regular, digital television. Jordan is the most bullish about high definition.

Broadcasters watched a taped, 10-minute block of TV clips all shot in the HDTV format. The clips showed sporting events like skiing and ice skating, scenery like the Grand Canyon, a roller-coaster ride, and national monuments such as the White House and the Capitol.

KLAS will broadcast the HDTV feed every half hour until the convention closes on Thursday.

That system KLAS is using is called the Grand Alliance. Once approved by the Federal Communications Commission, possibly later this year, it will be the system that all U.S. TV stations will use to provide viewers the next generation of television. HDTV systems used in other countries have been shown at previous conventions, but the Grand Alliance has not.

Westinghouse developed the special transmitter KLAS is using. Because it would cost about half the price of conventional transmitters, it should accelerate broadcasters' conversion to digital, said Paul DeGonia, director of HDTV development for Westinghouse's Wireless Solutions Co. Westinghouse's device will be ``competitively priced'' with transmitters developed by two competing companies, DeGonia said.

To receive the high-quality digital signals, viewers will need to buy new TV sets that won't be on the market for several years.

So as not to make all 220 million analog TV sets immediately obsolete, TV stations are supposed to simultaneously broadcast programs in both the existing analog format and the new digital one for 15 years. At the end of the period, stations will no longer transmit in analog. The Clinton administration wants broadcasters to complete the switch to digital in nine years, shortening the life of existing TV sets.

AT&T, General Instrument, the Massachusetts Institute of Technology, the David Sarnoff Research Center, Thomson Consumer Electronics, Philips Consumer Electronics and Zenith developed the Grand Alliance system.

Using the language of computers, digital technology is a vast improvement over existing analog. Digital is less susceptible to interference and is more efficient, allowing TV stations to pack four or five digital channels into the space of one analog channel.