Leaders of America's major nonprofit and charitable groups are expected to approve soon the formation of Independent Sector, a Washington group that would fight for preservation of voluntary giving to a multibillion-dollar sector of the country's economy.

Recommendations to establish the new organization were presented yesterday to representatives of charitable societies with a target date of Jan. 1 for starting the new venture.

The agreement to create Independent Sector is the result of negotiations over the past year by two umbrella groups for major charitable groups -- the Coalition of National Voluntary Organizations and the National Council on Philanthropy.

In effect, both groups would be merged into the new organization, if approved by member charitable societies.

Establishment of a permanent national agency on non-profits was recommended in 1975 by a privately funded citizens' panel called the Filer Commission, but the federal government made no response. The proposed Independent Sector would not be tied to government; indeed, the new group would have lobbying here as one of its functions, according to John Gardner, founder of Common Cause and chairman of a 26-member organizing committee.

Gardner said in an interview yesterday that Independent Sector would concentrate on public education about a little-recognized part of American society. "The American people don't know what they've got . . . it's unique in its reach and diversity," but facing serious problems caused by an erosion of private giving, he said.

No other country has an extensive nonprofit sector based on voluntary financial aid, and Gardner said one concern is to maintain the independence from government that comes with such support. Without an increase in voluntary giving, increased government support for the involved organizations is considered inevitable.

Organizations involved in planning the new group include the American Red Cross, Mental Health Association, National Urban League, U.S. Olympic Committee and United Ways of America -- itself an association of more than 37,000 agencies and social services.

United Way is the largest charitable organization -- with local affiliates raising more than $1.3 billion last year -- but there are up to 6 million such nonprofit groups in the country.

According to the Filer Commission, the charitable and nonprofit sector has outlays exceeding $80 billion a year, owns one-ninth of U.S. land, employs 5 million persons (6 percent of the work force) and has payrolls in excess of $36 billion a year (5 percent of all U.S. wages).

Gardner said Independent Sector would not be a trade association but rather a "forum to encourage voluntary support and service for the public good."

Problems are developing that make the nonprofit sector "less useful to society than it could be and in some danger of decline," including "inadvertent" threats to the freedoms of speech and assembly as manifested by the growing patchwork of local, state and federal laws governing independent organizations, mounting participation of government in setting the directions and agenda," Gardner declared.

Of agencies supported by United Way drives, 25 percent of average budgets already come from federal money, Gardner said. "Like those in the private sector," charitable group leaders are worried about "central rule-making in an enormous, diverse country . . . edicts from a middle-level bureaucrat," Gardner said of government assistance.

In addition to public education, research about the non-profit sector and regular publications, Independent Sector would do "some lobbying but a lot of communicating with government agencies," Gardner added. But the new group will stay out of issues involving specific groups -- many of which have their own associations already, such as the American Council on Education.

The mail goal is to increase private giving. Americans would give more "if they knew what an extra ordinary thing we have," Gardner asserted. Americans now give about $30 billion a year and contribute an unmeasured amount of voluntary time and services. About 80 percent of individual giving comes from families with incomes less than $20,000 a year -- partly reflecting the absence of tax incentives for families with higher incomes.