Big government, long the target of complaints from America's business sector, came under attack last week from the nation's leading philanthropies, many of them with headquarters near the seat of government here.

But the government, criticized for its tax laws and regulations, was not the only target. In addition, the American people were chastised for what is seen as an increasing reliance on Washington to fund all projects necessary for the good of society. This is seen as a threat to traditional American diversity.

Addressing the first national conference of a newly organized Independent Sector -- an umbrella coalition for volunteer and nonprofit educational, scientific, cultural and religious groups -- Rockefeller Foundation President Richard Lyman warned that strong forces "threaten the survival of the private non-profit organizations and of the philanthropy that sustains them."

The danger does not come from "blind or malevolent people out there" but largely from a "long, slow, but seemingly inexorable decline of [a] skeptical attitude toward government," Lyman said, adding:

"It may seem strange to call the growth of government's role inexorable, in a year when practically everybody seems anxious to curb the powers of government. . . . But if one takes the longer and wider view, it seems clear that popular expectations from government have been growing throughout the world for decades, and show few real signs of diminishing."

What Lyman and others find in danger, from this growing conviction that government is the solution to all problems, is a unique U.S. heritage among the family of nations -- an emphasis on volunteerism and private giving to support varied endeavors, from symphony orchestras and universities to scientific research and youth organizations.

In most countries, similar organizations survive primarily with government financing and inevitable government intrusion.

A key problem -- "a cause for some dismay," Lyman asserted -- is how few Americans know how unusual is this heritage.

Unless private groups can reverse recent trends, "We are in danger of letting pluralism deteriorate into a self-interested aggregation of groups no longer sufficiently bound together by common values, standards and aspirations to constitute a society," Lyman told a luncheon meeting.

The major trend that has affected charities adversely has been a factor that is crippling other sectors of American society: inflation. John W. Gardner, the founder of Common Cause and chief organizer of the new Independent Sector group, says contributions from private citizens have been plummeting because of higher taxes. While concerned also about the intervention of Big Government, Gardner is seeking aid from Congress in one way: He has voiced support for legislation to allow taxpayers to write off all charitable deductions and cited studies showing that, while the Treasury would lose $3.7 billion in revenues, private donations would jump $4.2 billion a year.

Andrew Heiskell, former chairman of Time Inc. and a board member of Independent Sector, suggested to the convention that the reason why charities finally had formed a single organization to promote their survival is that "the private sector is so threatened. . . . We are threatened first of all by relative declines in personal and corporate giving, along with a continued squeeze on foundations . . . by tax laws that remove some incentive for giving, especially by those who give most, those with incomes under $20,000."

At the same time, Heiskell warned that "the bogeyman of government" must be placed in a perspective that reflects a destiny to live with big government but not automatically to assume an adversary role. "As one of the few barriers to all-encompassing bigness, we do need a questioning, critical spirit," he cautioned.

Hospitals, medical research and higher education are among examples of sectors where government now dominates in financial support, having replaced private gifts. "The need for the large sums that only government can make available legitimizes its intervention," Heiskell stated, "but that intervention inevitably creates problems."

One example cited by Heiskell is uncertainty that accompanies federal money. He said Harvard University's School of Education has had federal funding sliced by two-thirds and "might not something similar occur at the medical school within the next decade?"

Independent Sector, organized last March after a decade of efforts, includes 125 groups such as United Way, Conservation Foundation, Epilepsy Foundation, National Audubon Society, National Urban League and the United Negro College Fund.