With the word that all-news radio station WTOP-AM is on the market for an asking price of around $8 million, rival all-news WRC-AM hustled on the air with a "live-line" phone check on the report with Joel Chaseman, president of WTOP's parent Post-Newsweek Stations.

It was more than a news item for Frank Barnako Jr., who has been doing business reports as a sideline. Baranko also happens to be news director at WRC, one of three stations scrapping for the 10 per cent chunk of the Washington radio market that tunes to non-stop news.

The field of three competitors soon will be narrowed when WAVA-AM-FM, the feisty independent that pioneered all-news radio operation here, changes format to gospel and contemporary music once the Federal Communications Commission grants approval. That would leave WRC, the NBC flagship outler in the nation's capital, squared off against WTOP, the CBS affiliate.

And then perharps there will be only one?

"We've been eyeing each other across the fence," says Barnako. "WE both seem to have loyal and devoted audiences that can't be wooed away by the other."

There has been static about the future of both WRC and WTOP as all-news radio stations. It depends on which rumor your turner picks up.

"You better write the story before we're the only one left," says Barnako, a hustling news director whose pace is echoed by his station's on-air sound.

"I don't think that anyone should get his hope up too that a new owner would change our all-news operations." says Peter Lund, WTOP's general manager and vice president.

A sale just might lead to a switch from the WTOP's all-news format - most expensive in radio programming, requiring a hefty staff of reporters, writers, editors and back-up staff. WTOP, Lund says, has been "marginally profitable" as the leader in the local field.

In about three years, NBC has spent in excess of $3 million to tool up WRC as its only non-stop news station.

The network's commitment remains firm, Barnako empahasizes. But earlier this year, NBC folded its news and information service sold to affiliates because not enough affiliatesd signed up to make it profitable. The network has beefed up WRC's news staff and coverage to fill the gap. But the question remains: How long will NBC give its only all-news radio station to turn a profit?

Chaseman, who is a vice president of the Washington Post Co. as well as head of its radio and television operations, confirms that WTOP-AM, the company's single remaining radio station, has been listed with Howard Stark, a broker. Post-Newsweek Stations sold its Cincinnati AM outlet last year and said then that it wanted to put its emphasis on television.

Stark, a New York-based broker, said the decision to retain or change WTOP-s all-news operation would be up to a new owner. He denied that has has been pushing a switch, as has been reported in a published rumor.

"But the option is open since there is the prestige of operating in the nation's capital."

The three all-news radio stations have divvying about a 10 per cent slice of the area radio market. One survivor undoubtedly could turn a comfortable, if not lavish, profit.

"One here would be just fine," says Lund. "But I don't think it is impossible - difficult but not impossible - to have two profitable all-news operations."

In other cities. like Philadelphia and Los Anglese, all-news stations have attracted more than the 10 per cent market in Washinton. One very good reason that the slice is smaller here is that WMAL-AM, the reading station, has good news coverage along with its music.

In the last audience-poll figures, WTOP had about 433,000 listeners, WRC nearly 300,000 and WAVA around 217,000. That's the estimate of the number of listeners in a given week from 6 a.m. to midnight.

The late-entryWRC non-stop news caught up with WTOP in January and February this year for the first time but then fell back in April and May.

The size of the listening audience is important because it determines the advertising rates that a station can charge. And that is where the profits are.

All-News radio depends on some simple truths of human nature: Most people curious about what is going on around them and like to be among the first to hear the news. It was ZTRA, a small radio station in Tijuana, Mexico, that started it all in 1958 by beaming non-stop news over the border to Los Angeles and San Diego.

There probably haven't been more than 20 or so all-news stations operating at a time in the United States. When WBC started up in 1975, Washington become the first city to have three all-news stations.

Surveys indicate that the average person probably listens to an all-news station about 35 minutes at a time - although there are addicts who keep tuned for hours. The prime time is the morning drive-to-work hours when audences are the biggest.

In 24 hours, an all-news radio station can spew forth upwards of 250,000 words of information, about what you get in three or four full-length novels.

To break the repetitiveness of recycled news, all three local all-news station interspers features and commentary. Along with breaks for weather, time, sports, Wall Street reports and traffic updates, there are gardening and cooking tips and other service features.

"Cope is the word around here now," says WTOP's Lund, "We want to help people get through the day."

Both WRC and WTOP are proud of special series their reporters.WTOP looked into the occult for one series and housing in Washington for another. WRC won an award for its report on the Ku Klux Klan.

Both Barnako and Lund are jockeying for WAVA's audience when the Arlington stations leave the all-news competition. A couple of months ago WTOP began using a traffic helicopter as WAVA has been doing to inform its heavy concentration of Virginia listeners of the traffic situation on the Potomac bridges. WRC will take over Ronald Reagan's commentary from WAVA.

The WAVA AM-FM stations are to be sold for $2 million under an agreement conditional on FCC approval.

Arthur W. Arundel, who pioneered all-news radio on WAVA starting in 1961, has agreed to sell both the Am and FM operating to a group headed by Alexander W. Sheftell. Under the application files with the FCC, the AM station will be spun off and sold to an Indiana-based network that specializes in gospel messages. Sheftell is to keep the FM station for a "contemporary" music sound.

And that will leave the all-news field to WRC-AM and WTop-AM in a non-stop war of words.