Standing before a group of 100 national business leaders at the White House in late March, President Reagan extolled personal enterprise and self-reliance as the keys to rebuilding America today.

He was there, he added with his famous grin, to ask for their money and support.

"We want to rebuild America, not from the government down, but from the people up. All of us, together as partners, community by community," Reagan told those he hopes will lead his campaign for private-public partnerships.

Before Reagan's arrival that day, Vice President George Bush greeted the business people and introduced the administration's appeal for increased corporate philanthrophy to support community and social programs.

"Not that we think government has no role in helping," Bush said. "But we also know the best answer, in terms of employment, in terms of dignity, is to see the private sector as vital.

"And it also is just a wonderful kind of ethic to think you're involved in something where just one human being, one organization, is helping people to have a better life . . . this is what drives it."

But whether private-sector dollars can fill the void created by the removal of nearly $4 billion in federal funds for social services is a matter creating much debate across the country.

The administration's view is being criticized widely by nonprofit organizations that say they will be unable to offer their services if federal funds are cut.

Even if private funding were to increase to the levels anticipated by the administration, some social-program directors say, their services will be crippled in the interim and left to fend for themselves, competing later with programs of greater visibility and popularity.

Others, particularly in the arts, complain that budget cuts force them to extend fund-raising periods in an effort to obtain most of their general operating costs.

To promote his private-public partnership ideals, Reagan has appointed the President's Task Force on Private Sector Initiatives to oversee formation of public-private boards at the local level to help meet the social and economic needs of American communities. The Task Force is composed of 44 business and community leaders, headed by Armco Inc. Chairman C. William Verity Jr.

Verity, 1980 chairman of the U.S. Chamber of Commerce, and Task Force Executive Director Jerry A. Guth are on corporate loan from Armco. Other task force members are United Way President William Aramony, Archbishop of New York Terence Cardinal Cooke, AFL-CIO Community Services Director Kenneth N. Dayton, Delaware Gov. Pierre S. duPont, Sen. David Durenberger (R-Minn.), Rockefeller Foundation President Richard W. Lyman, Kaiser Aluminum and Chemical Corp. Chairman Cornell C. Maier, Times-Mirror Chairman Frank D. Murphy, National Association of Manufacturers Chairman Alexander Trowbridge and CBS Inc. President Thomas H. Wyman.

According to Verity, local public-private partnerships will be encouraged to identify important needs in their communities and then marshal human and financial resources from private and public sectors to meet those needs.

Verity plans to tap all the traditional organizations: civic and religious groups, business and labor, service clubs, voluntary organizations, educational and philanthropic institutions, trade and professional associations, neighborhood organizations and others.

"We are looking for reevaluation of community social programs to find overlapping and waste," he said. "When a community now looks at its needs, they may be different from what the federal government thought they were going to need." He said the task force will be working closely with mayors and governors to implement the White House's program.

"As we cut back on the federal government doing these things, the private sector must become more involved," Verity said, emphasizing long-term commitment and "corporate social responsibility," a relatively new phrase in fund-raising.

Corporate giving in 1980 averaged less than 2 percent of corporate pre-tax income.

But since last spring, three major business trade groups, the Business Roundtable, U.S. Chamber of Commerce and the National Association of Manufacturers, have issued position papers urging all businesses to adopt philanthrophic programs as "good business practice."

James Keogh, the Business Roundtable's executive director of information, said there has been a great deal of interest and inquiry about the group's paper, but added that his organization does not attempt to monitor what member companies are doing.

NAM also had a good response to its position paper, which encouraged members to take advantage of the new tax law allowing corporations to deduct charitable contributions of up to 10 percent of their taxable income.

A statistical breakdown of private U.S. philanthrophy by the American Association of Fundraising Councils indicates that corporate giving amounted to $3 billion in 1981, with foundations providing an additional $2.62 billion, bequests of $3.49 billion, and individual giving of $44.51 billion. The total charitable contributions for 1981 totaled $53.62 billion.

Philanthropy analysts at the Conference Board, an independent, nonprofit business research institute, said the prospect for increased corporate contributions are tied to profits.

Conference Board Executive Director E. Patrick McGuire said one has only to look at profits from the last quarter to guess what impact depressed earnings in many sectors will have on much corporate giving. As an example of the trouble industry is in, U.S. business failures are heading toward their highest point in nearly 50 years.

National unemployment figures have continued to rise, forcing more people to seek aid rather than give it. In turn, a growing number of local emergency assistance groups report a dramatic increase in requests for help, but say that funding cuts render them unable to cope.

This spring, the Independent Sector, a coalition of national voluntary organizations, corporations and foundations, released a detailed analysis of the President's economic recovery program and its direct significance for philanthropic and volunteer organizations and the people they serve.

The report predicts substantial increases in giving by businesses and individuals, but cautions that the administration has "unrealistic expectations for what private philanthropy and voluntary organizations can do."

At the conclusion of the 1981-'82 United Way drive, National Chairman Donald V. Seibert, who has consistently supported the administration's program said, "It would be foolhardy to think that private philanthropy can make up for the government cuts."

Seibert did, however, forecast an increase in corporate and private philanthropy, saying that "the corporate sector is very aware that it has been asked to assume a greater responsibility for achieving societal goals."

Seibert has been similarly optimistic about individual giving. About 68 percent of United Way contributions are from individuals.

But others say the Economic Recovery Tax Act of 1981 discourages contributions by reducing or eliminating the incentive many high-income taxpayers have to give to charity.