The one-hour documentary may become an endangered species on commercial televison as ''maxi-docs'' move into prime-time scheduling. ''ABC News Closeup,'' which already had its number of yearly hours decreased, has just announced another radical change in direction. Instead of the usual one-hour documentary, ''ABC News Closeup'' will celebrate the start of the new school year on Sept. 4 with a three-hour examination of the imperiled future of US education: ''To Save Our Schools; to Save Our Children.''
It's the opening gun of the most recent coup at ABC News, in the movement to overthrow the long-term supremacy of the one-hour documentary and substitute an 8-11 p.m. series of ''maxi-docs'' that occupy the entire three hours of regular prime-time TV. Although such long-form documentaries have been done by all three networks now and then, this is the first time they have been announced as a definite series. They are already being identified in the broadcast industry as ''blockbuster'' documentaries.
The prime mover behind the new long-form format - with ABC News president Roone Arledge giving wholehearted encouragement - is Pamela Hill, vice-president and executive producer of the ''Closeup'' documentary unit. I lunched with Ms. Hill recently, during which this seemingly fragile but energetic and totally committed news person - who has won many awards since she joined ABC News in 1973 - was able to communicate a sense of excitement and anticipation about the new direction for her organization.
''Since we'll be doing the long-form documentaries only three or maybe four times a year, we can put a great deal of care and attention into them. Part of the decision came out of my feeling that, even though we were handling quite serious issues in the hour form, some of the most important issues of our time were really just not being looked into in the proper depth.
''They were of a scope that required more than one hour.'' According to Ms. Hill, a presidential commisssion report revealed that some 80 percent of high school students cannot write a minimally intelligent essay; 13 percent of today's high school graduates read and write at sixth-grade level; SAT scores plunged to an all-time low in 1980. ''I mean, you can't cover the demise of the American school system in a single hour. And you certainly can't investigate all aspects of our nuclear future in a single hour. Can you?''
Ms. Hill says she began to think of television's role in telling the American public what is really important over a long period of time. ''We inform them of what's happening on a daily basis, but not about the issues they should be paying attention to regularly, issues which may affect the quality of their own lives, issues that affect the way they live and the way their kids grow up.
''And it was that kind of perception that led me to talk to my own management about going in the long-form direction. They were very supportive and enthusiastic about it.''
Ms. Hill is one part of a famous journalistic couple (her husband is Tom Wicker of the New York Times), and through their individual contributions they have had a strong influence on American political attitudes. She reveals that their second ''blockbuster doc'' will concern the US Supreme Court, its changing role ''and a whole horizon of problems that were once considered private . . . the right to die, the right to have children . . . etc. There will also be a long-form documentary sometime in the future which takes a look at America's permanent underclass, poor people who are having difficulties breaking loose from their poverty.''
According to Ms. Hill, one of the most exciting of the ''blockbusters'' will cover our nuclear future - ''the whole range of nuclear issues that we're going to be facing as we approach the year 2000 . . . nuclear waste, nuclear arms races, nuclear proliferation.''
We also discussed the comparatively recent phenomenon of the television news show that makes money: During Ms. Hill's early years with NBC White Papers she recalls that there was very little thought of profitability. The shows were done as a public service. Then, along came ''60 Minutes,'' whose commercial success changed all the networks' outlooks on news as a moneymaking commodity.
''While I think it's great to make money on public affairs, it is also important for all of us in network news to remember that not every program can be profitable. Sometimes a network has to make the decision to put on something which is needed by society, whether or not it results in an immediate monetary gain.''
All the commercial networks are committed to do a certain amount of public-service broadcasts, even though it often means low ratings on those nights. But mightn't some skeptics interpret the three-hour format as an easy way to get three public-service hours out of the way quickly?
Ms. Hill shrugs and says, just a little sadly: ''You know, documentaries are expensive. Mostly they lose money. One can cost as much as $500,000 for an hour, and the three-hour show could triple that cost. It's an expensive solution, wouldn't you say?''
Expensive, but brave and essential, too. The push to lengthen public-service broadcasts appears to be one of television's most constructive moves in recent years, providing the American people with a solid menu of information rather than just the short, sweetened dessert we have become accustomed to in our documentaries.