Washington — ''One of the great problems for television news today is the public's distrust of it,'' says Lawrence K. Grossman, president of the Public Broadcasting Service (PBS) since 1976, now scheduled to become president of NBC News next May.
In an interview at PBS headquarters here, Mr. Grossman indicated he is troubled by the political antagonism toward the news business which he sees in Washington. Equally disturbing, he said, was the public's lack of support for the network news organizations when they protested the Reagan administration's restraints on news coverage during the early days of the Grenada invasion.
''The big challenge,'' he says, ''is to restore confidence in the reporting process. It has been sadly undermined.''
For several years before he left his own advertising and production company to join PBS, Grossman was vice-president in charge of advertising at NBC. Although he lacks specific news-gathering experience, Grossman is admired by many television newsmen because of his instrumental role in public television's growth as a leader in broadcast journalism.
Under his aegis PBS's ''Frontline'' became television's only weekly documentary series, and ''Inside Story'' became television's only regular series about the media. Grossman was an originator of one of TV's most highly praised public-information series, ''Vietnam: A Television History.'' He is also said to have played a major role in the expansion of the ''MacNeil/Lehrer Report'' to the one-hour ''NewsHour'' format.
Does Grossman worry about his lack of experience in the news field?
''I don't make any bones about the fact that I've never had any professional journalistic experience on a top level,'' says Grossman, speaking in a softly modulated accent that just hints of his Brooklyn-cum-Columbia University background.
Grossman plans to go to NBC no later than March 1 but will not officially take over from current President Reuven Frank until May. ''That will give me a perfect opportunity to watch and learn. Reuven will continue to have the managerial responsibility for the presidential election coverage through the conventions. I'll be looking very hard.''
There has been much talk about network news going to one hour, but the major opposition comes from the affiliated stations. Since Grossman played an important part in convincing PBS stations to agree to carry the ''MacNeil/Lehrer NewsHour,'' can it be assumed he may play a similar role at NBC?
''It's very clear that much of what has happened at PBS - the working out of things with the stations themselves, not dictating or imposing, but developing on a joint basis - is probably what would have to be done at a commercial network. Perhaps that will stand me in good stead. But, obviously until I go over there and learn more about the business. . . ''
He indicates this watch-and-wait policy holds for NBC News personnel as well, despite the rumors that MacNeil might be wooed away to NBC. ''It would be irresponsible of me to raid PBS personnel.''
Grossman is coming into a news organization that most of the time ranks third in a field of three. Has there been any pressure on him to move it up to No. 2 or No. 1?
''In all of my discussions with Grant Tinker (NBC chairman of the board) and Thornton Bradshaw (RCA chairman of the board), nobody has ever said that my mission is to make NBC No. 1. I'd love to be No. 1. I'm a big competitor. But, they're more concerned with a strong organization, a powerful news presence, quality news operations. That's the only discussion we've had. But that's not to say that they wouldn't give their eye teeth to be No. 1.''
Grossman says he has always felt that it is in the interest of the commercial networks to make sure that PBS is strong. A strong and effective broadcast system needs duality - private as well as public, he says.
''We're already seeing a lot of interchange. It was ABC News, after all, that put up the initial outside money to make the Vietnam series possible.''
Won't Grossman miss being part of PBS?
''Sure. It was a very tough choice for me and I really agonized over it. I think PBS will continue to be a vital force in American society, and I was looking forward to participating in it.
''But NBC was too much of a challenge. TV news has a major impact on our society. And I think, just as I brought the kind of discipline that comes from operating in a commercial world to Public Broadcasting, I can bring some of the PBS idealism and sense of public service to commercial TV.''
A five-person committee is now trying to find a successor to Lawrence Grossman. He says PBS hopes to have somebody in place in time for its annual meeting March 29.
''I think it's of great importance that it be done quickly,'' he says, a bit sadly. ''Organizations don't run well on hold. PBS needs a leader.''
If Lawrence Grossman were asked to list the three major credentials necessary for the job of president of PBS, what would they be?
''First, a feel for and a love for broadcasting. A sense of the medium.
''Second, a dedication to bettering the human condition.
''And third, a sense of humanity. The ability to work with people, to help people enjoy working together, to give them the opportunity to do their best.
''I think a lot of the things for which I've been given credit are things that have been initiated by and carried out by others. The only credit I would like to take is setting the atmosphere, providing the environment in which they could do their best work.''
And the three major credentials for the job of president of NBC News?
Larry Grossman thinks for a moment, rubs his neatly trimmed beard, then smiles. ''Exactly the same!"