Big broadcasters join up to push their version of teletext TV news service

In an unprecedented show of cooperation for the broadcast industry, CBS, NBC, and Group W combined forces Wednesday to stake a further claim for the future of their own form of teletext.

Their teletext is based on the North American Broadcast Teletext Specification (NABTS) system. Teletext is a text-type broadcast news service, delivered over regular television channels. It does not require a cable connection.

In a news conference at New York's Helmsley Palace Hotel for hundreds of electronic media reporters, CBS announced the inauguration, yesterday at 6:20 p.m., of ''the nation's first local and network broadcast teletext service, called Extravision,'' on WBTV, the CBS Network-affiliated station in Charlotte, N.C. NBC and Group W reminded the assmbled reporters that they, too, are in the NABTS business.

Already in existence, although strictly national in content, is Group W's NBC service in Charlotte. According to CBS, its system is superior mainly in that it allows for excellent full-color graphics and integrates local news into its format.

Taft Broadcasting operates a teletext service in Cincinnati, based on the British World System, rather than the NABTS; NABTS is an extension of the French Antiope and Canadian Telidon systems. The battle for international acceptance between NABTS and the British system is what this basically promotional press conference was all about.

Although Panasonic representatives at the press conference announced that a decoder would be made available in Charlotte at a $300 promotional list price, it was also disclosed that the decoder could function only with TV sets that are equipped with an ''RGB'' (Red-Green-Blue) connection. This connection is now available on a small minority of standard sets and is required for most computer plug-ins.

Panasonic is also selling a $1,200 list-price teletext monitor in Charlotte. A Panasonic spokesman speculated that ''sooner or later'' the decoder would probably be standard equipment on most TV sets.

An electronics expert in the audience estimated that the cost to the manufacturer would be as little as $50 additional. Other manufacturers are already marketing RGB-ready sets.

Both CBS Extravision and NBC Teletext are advertising-supported services, free to the consumer. They utilize a portion of the regular TV signal not currently being used.

The Extravision launching in Charlotte will probably be seen mostly by customers in television stores, since almost no decoders are yet in the hands of consumers.

''Remember the early days of television?'' one of the Charlotte TV executives reminded the conference. ''The sets were sold at public demonstration sites. You have to give people something to see first before you can expect them to buy.''