"In political campaigns," muses Frank Mankiewicz, "I used to like to spend as much money as possible on radio."

Now, Mankiewicz is president of National Public Radio, and part of his job is getting money out of politicians.

He sits in shirtsleeves behind the big desk at NPR, his chunky frame oscillating busily between the bright yellow typewriter, the intercom and the telephone. Bright Corita Kent posters proclaiming love, peace and social justice are splashed across the wall, reminders that Mankiewicz, 54, was once the press secretary for Robert Kennedy and later campaign manager for George McGovern.

An FM tuner behind his back pushes a very mellow sound through the loudspeakers as Mankiewicz is busy on the phone:

"Come on down," he says, "we're right across M Street from CBS, and we'll be happy to show you around."

He hangs up and turns to an assistant: 'We're going to have some corporate visitors who want to give us some money. I think there's $200,000 in it, and with matching grants that comes to $400,000."

In network television, that kind of money might get a couple of commercials briefly on the air. At NPR, it's 5 percent of last year's budget, nearly 10 percent of the budget for 1976.

At first glance, Mankiewicz seems an unlikely choice to head an organization that produces broadcast material for 217 noncommercial radio stations, ranging from the award-winning "All Things Considered" to "Jazz Alive" and a Shakespeare festival that is running in four parts this month.

"I don't think they hired me for my management skills or for my nonexistent experience as a broadcast executive," he cheerfully admits.

What he was hired for, he believes, was "to get more money, but mostly to get more recognition -- increase general awareness of public radio. I think they wanted me to make waves -- to raise less corn and more hell."

That's a significant change, and Mankiewicz -- after 18 months on the job, during which the budget has risen more than 50 percent and NPR has taken on a satellite system -- is both a symptom and a catalyst.

"I know a lot of people around here who were getting ready to walk out until they heard Mankiewicz was taking the job," says one NPR staffer. "Now they're not only staying, but they're excited."

There was some initial grumbling that Mankiewicz seems more interested in news than in cultural programming, and some dismay at his lack of radio experience. Telephone Executive

"I was worried at first," says one former employe who quit and went into TV after seven years at NPR. "His appointment looked like a very political thing -- and I watched him closely. He has an annoying habit, if he sees you standing around, of calling you into his office for a chat and then letting you sit there for 20 minutes while he answers the phone. That way, you get to see him in action, and I really came to admire the way he operates.

"If he has a weakness, it may be that he is too open, too candid -- those are not always unalloyed virtues in an executive."

Mankiewicz took over in August of 1977, a little more than a year after a network crisis in which 15 members of the news staff threatened to resign. He says he knows of no connection between that crisis and his arrival -- like most Americans, he was only marginally aware of NPR's existence when the trouble broke out. But NPR old-timers see it differently.

"Mankiewicz represents a complete turnaround in NPR's management philosophy," says one. "Formerly, the idea seemed to be that if we were very quiet and nobody noticed what we were doing, perhaps a lot of people would be able to hang on long enough to collect their pensions."

This feeling grew during the later years of the Nixon administration, when news became a volatile and sometimes dangerous commodity.

"That was a very nervous time," recalls news commentator Linda Wertheimer, whose voice is well-known to those who heard NPR's epic broadcasts of hearings on Watergate and the Panama Canal Treaty. "We got away with a lot because people didn't notice us."

NPR began on a small scale in May 1971 with a 90-minute news program "All Things Considered" and a few short syndicated features. The coverage of hearings began soon afterward and NPR began to grow. On its first anniversary, it was offering about 22 hours of programming per week to 130 member stations, and "All Things" had already won a Peabody Award.

But for years, it remained the "orphan child" of the Corporation for Public Broadcasting (which allots government money to noncommercial broadcasters) with less than 10 percent of CPB's funding, the bulk of which went to public television.

"When they interviewed me for this job," Mankiewicz recalls, "they asked me what I would do if I were president of NPR, and I told them, 'I would do whatever is necessary so that people like me would have heard of it.'"

Now, according to Roper surveys, it's beginning to happen: Nearly everyone now has an FM radio ("70 percent of new General Motors cars, I have heard, are being equipped with FM," Mankiewicz says), and a higher proportion of the growing FM audience is tuning in to noncommercial radio. The Listening Elite

One of Mankiewicz's goals is to rid public radio of its traditional elitist image without debasing the content. "We're finding that as our audience grows, its characteristics become closer to the general audience," he says. "They're poorer and less educated than they used to be. Our listeners are now 10 percent nonwhite, and last year this was the fastestgrowing part of our audience."

NPR is not as ratings-conscious as the commercial networks, but uses the annual Roper poll, which tests both awareness of public radio and actual listening habits. The increase in black and Hispano-American listeners is variously interpreted at NPR. Some feel that it reflects growing emphasis on special-interest material, from the White House Jazz Festival (and other live jazz material) to the Panama Canal hearings. The hearings probably increased Hispanic- American awareness of NPR -- now also encouraged by some Spanishlanguage programming.

"We're not concentrating our efforts on any specific group," says Sam Holt, senior vice president for programming, "but we are definitely trying to approach the national average."

"It just ain't true that an 'alternative' medium has to mean 'highbrow,'" Mankiewicz says. "You offer good programming, and people will listen."

The reason he liked to use radio in political campaigns was that he believes people have a feeling about radio that they don't have about television. "People who listen to radio are usually alone," he says. "I can't watch television when I'm alone, but I can listen to the radio.

"There is a one-to-one relation between the listener and the voice that you don't get with television. If radio could have been invented after television, it would be the rage now. It's so convenient -- you don't have to sit down and watch it, and you can take it into the kitchen or to the beach or listen in your car. The radio audience is going up, while the television audience is flattening out.

"Another thing is listener loyalty. On television, people watch programs -- nobody's watching stations. Where- as in radio they will say, 'Hey, let's punch up the country-and-western station -- or classical music, or jazz, or all-news. They tune in to a particular sound and radio stations have taken advantage of that trend. We're the only radio stations now that are doing more than one thing. You lose listeners that way -- the classical music people tune out when you put on jazz. But they come back."

On the other side of the street, commercial radio seems to be booming. Business Week estimated recently that radio advertising will gross nearly $3 billion this year. Network commercial radio takes only a small slice of that big pie, but last year's slice amounted to $160 million. Changes in the Competition

Mankiewicz dismisses such competition with a snort: "At NBC, they think that network radio programming is playing the top 40 on all stations at the same time." But that picture is changing, too. NBC, spurred by Fred Silverman, is reorganizing its radio operations.

At CBS, where the nightly "CBS Radio Mystery Theater" recently began its sixth year, a new series, "Sears Radio Theater" is being launched five nights a week under the sponsorship of Sears, Roebuck.

CBS Radio president Sam Cooke Digges is bullish: "It's a fantastic medium and coming back strong. It's really instant in terms of breaking news, and for drama people are beginning to do again what they did in the old days -- sit around the room and look at the radio."

As NPR grows, Mankiewicz expects to see more member stations specializing, as the number of public stations in a given listening area multiplies. Right now, NPR has only reached a small fraction of its total potential membership -- 217 out of the 984 noncommercial radio stations in the United States. But the country is fairly well covered: Approximately 70 percent of the American population is within reach of at least one NPR station, and when New Jersey gets a station in the near future, Idaho and Hawaii will be the only states with none.

NPR predicts growth of about a dozen stations per year for the next three years -- and a higher rate there- after -- despite the stringent membership requirements: To join NPR, a station must have at least seven fulltime employes, a budget of $100,000 or more per year, and at least 18 hours of programming per day.

It must also pay annual dues which vary according to size but average between $3,500 and $4,000 per year. For the money, they receive 18 regularly produced features, averaging about 40 hours of programming per week, as well as coverage of special events such as congressional hearings and last year's White House Jazz Festival.

Some of the specials NPR is developing for its member stations:

Half-hour prologues to the PBS-TV Shakespeare series.

Live coverage of the Los Angeles Philharmonic, beginning in the spring, to complement NPR's exclusive live coverage of the San Francisco Opera.

A new Masterpiece Radio Theater to begin in May, and include "Anna Karenina" and "Moby Dick."

A two-hour morning news service to match the evening's "All Things Considered."

And in 1980, a 12-part series, "A Question of Place," with portraits of such artists and thinkers as James Joyce, Bertolt Brecht and Claude Levi-Strauss.

This spurt of activity reflects NPR's budget boost as well as Mankiewicz' sweeping changes in top management. The annual budget ($3.2 million in 1973 and $8 million last year) has gone up to $12.5 million and is still climbing. NPR's share of the government funds distributed by CPB has gone up from 9 to 19 percent and will soon be 25, and the proportion of corporate funding for the network is also going up. "We used to get about 75 percent of our money from the government," Mankiewicz says. "Now it's down around 67 percent, and I'm hoping to get it down to 50."

In most countries with government- supported broadcasting, radio gets 20 to 30 percent of funding -- a ratio the U.S. is just beginning to reach, partly because public television was much more organized than public radio when CPB was established. The radio and TV allotments are periodically readjusted by CPB.

Part of the increased NPR budget reflects Mankiewicz's skills as a lobbyist with CPB; part reflects the growth in NPR membership, and part results from matching-fund grants from CPB (subject to a congressionally imposed ceiling). Satellite Future

The next growth phase for NPR will begin later this year with a satellite transmission system allowing the network to broadcast directly to member stations without using the long telephone lines it now rents. Eventually, NPR will be able to transmit on as many as 20 channels simultaneously, vastly increasing the options available to member stations.

"Right now," says Mankiewicz, "we transmit live via one crummy 5-kilo- cycle telephone line, and the sound quality is not good -- we have to tape music programs and send them out by mail.

"The satellite will change all that. We will be able to transmit in stereo, and the quality of the sound is incredible -- full range and no pops or crackles.People will have trouble, at first, believing it's a live transmission, and I told our engineers they should add some static to make it more credible.

"I used to know a mess sergeant who would crush ping-pong balls and put them in the powdered eggs. It's the same artistic principle."