A conservative bunch, the stewards of America's national forests generally are not the type to argue for "a radical new approach" to anything, let alone the environment. But yesterday the head of scientific research for the U.S. Forest Service pledged a new era is about to begin.

From now on, government scientists promise to approach forests not as a standing cash crop but as a complex and still mysterious ecosystem.

"What we've got to do is embrace a much larger view of what a forest is," said Jerry A. Sesco, deputy chief for research at the Forest Service. Sesco said the Forest Service needs to adopt "a new environmental paradigm" that recognizes the role of forests as havens of biological diversity and an indicator of the general health of the planet.

Sesco was responding to a report issued by the National Research Council, which concluded forest research was underfunded, narrow and often uninspired, failing in general to answer some of the most basic questions about the natural workings and well-being of America's forests. The report was released yesterday at the annual meeting of the Society of American Foresters here.

The panel stated that just as "concern about the global role and fate of forests has never been greater," research on forests is inadequate and outdated.

While it is not unusual for the National Research Council to issue reports calling for more research, the conclusions of "Forestry Research: A Mandate for Change" were unusually critical.

The panel of experts who wrote the report said "the existing level of knowledge about forests is inadequate to develop sound forest-management policies" and "inadequate to meet society's needs." It concluded "forestry research must change radically if it is to help meet national and global needs."

The research council panel noted the Forest Service budget for research has dropped in buying power by about 15 percent in the last decade. Competitive research grants, in which independent scientists submit applications and fight for their approval, have been eliminated at the service. In 1980, there were about 1,000 Forest Service scientists. Today, there are 740. Facilities are outdated. Modern scientific equipment is sparse. And fewer and fewer students are choosing forestry as a career.

Forestry specialists place much of the blame on the Reagan administration, which believed that new research was not necessary and that past scientific studies could be taken off the shelf and spruced up when needed.

John Gordon of Yale University, who chaired the National Research Council committee on forestry research, said Forest Service scientists, in essence, can not see the forest for the trees. Overall, the agency has concentrated its efforts on growing more trees faster, not on understanding the interplay of species, or studying the role that forests play in regulating climate.

While a concentration on production -- or what amounts to tree farming -- was probably appropriate during the building boom following World War II, Gordon said "the number one job today is creating a liveable environment."

Sesco said that the Forest Service was moving toward a more interdisciplinary approach that focuses more on the total environment and less on tree production. "I assure you we are going to do everything we can to heed the recommendations of this report," Sesco said.

"What you were hearing today is nothing short of a revolution," Gordon said.

Gordon and his colleagues recommended increasing the research budget for the Forest Service by 10 percent for the next five years, from a 1988 level of $135 million to $218 million. The panel also advocates boosting the so-called McIntire-Stennis funds alloted for forest science by the Agriculture Department from $17 million annually to $109 million over five years.

The panel warns that, with money tight, such increases will only be realized when the Agriculture Department changes its funding priorities. Traditionally, the Forest Service and its scientists have taken a backseat at the Agriculture Department.

"I think the change is real," Gordon said, conceding there would be "plenty of friction."

"But society is demanding more research on the role of forests and better understanding on where forests fit into the total picture. They're not demanding more research on growing trees."