"There are only three things you can do with money," says Obie Benz, former antiwar activist and heir to a food fortune.

"You can spend it. You can reinvest it. Or you can give it away."

Since he turned 21 seven years ago and came into possession of a large sum of money - he won't say how much - Benz has made giving away money a full-time job.

In the San Franciso Bay area, Benz put together the vanguard Foundation to support social change, and the organization now spends more than $300,000 a year on such efforts as prison reform, support for counterculture newspapers, legal services for migrant workers, the Gray Panthers and women's rights.

He is one of a small, but growing, number of young Americans who have inherited vast sums of money and elected to use the funds in an attempt to create social change.

Since Benz organized Vanguard, rich young activists have put together similar foundations in Boston and Los Angeles, and two are being organized in New York and Philadelphia.

In the world of foundations and private philanthropy, such efforts are drawing increased interest and attention as the man and women who control the vast resources of the nation's 26,000 private foundations ponder how best to spend their dollars.

Meeting in Washington recently, representatives of most of the largest and wealthiest foundations debated that issue for four days, many of them arguing that the way of the future for private philanthropy lies increasingly in the realm of supporting social change.

With increased federal dollars comitted to education, medical research, welfare and science, they said, many of the activities once supported chiefly by private donations now have the government as their main benefactor.

"If we do the same things the government does, we run risk of being redundant," said Kirke Wilson, executive director of the Max L. Rosenberg Foundation of San Francisco.

"The question the becomes, 'Why should foundations exist?'

"If you're doing the same things that the government is doing, it's very hard to make a case that you're doing better. But if you're doing something the government isn't doing, you run the risk of doing something nobody thinks is important."

"To do some good is relatively easy," said Landrum R. Bolling, chairman of the Council on Foundations, in a report to the membership at last week's meeting. "To do the really significant will take all the wit and wisdom we can acquire."

"One role of the foundations can be to develop and support programs that are too risky for the government to try," said James L. Kunen, president of Washington's Eugene and Agnes Meyer Foundation.

"The government can't afford to fail. We can," added the Rosenberg Foundation's Wilson. "It's very hard for some bureaucrat to go up to Capitol Hill and admit to Congress that one of his programs just didn't work."

Wilson, like many other foundation directors, is currently into supporting organizations that are suing the government over a variety of issues.

He is funding one group that is blocking large land accumulations in California's Westlands Water District with a lawsuit and a federal court injunction against the Interior Department's Bureau of Reclamation.

"We monitor the government to make sure they obey the law, and when they don't obey the law, and when they don't we sue them, said Robert Johnson, execuitve secretary of Chicago's Weilboldt Foundation.

It is currently supporting several lawsuits aimed at curbing governmental surveillance of community groups. Those lawsuits were undertaken shortly after it was discovered that the head of one of the community organizations the foundation was supporting was a Chicago policeman spying on the group from within.

Throughout the course of the four-day meeting here, there was a constant recurrance of the theme of lack of confidence in the ability of government to solve human social problems despite heavily federal spending.

"There's no denying that people today are wary of government solutions," Bruce K. MacLaury, president of the Brookings Institution, told the foundation officers.

"We cannot solve all human problems simply by throwing federal dollars at them, hiring more civil servants, having them set up and apply more controls and provide more services," said Coucil on Foundations chairman Bolling.

The Vanguard Foundation is a good illustration of Bolling's point. Organized in 1972, it took in $70,000 its first year of operation. In 1977, it took in more than $400,000 and it distributed more than $300,000 in grants and loans.

"It's morally right for People with inherited money to use some of their god luck and good fortune to support those organizations working towards a greater redistribution of a wealth and power," said Benz, a New Jersey native who graduated from Vermont's Middlebury Coleege in 1971.

To spread that philosophy around the country, Vanguard is in the process of publishing a pamphlet artitled "Robin Hood Was Right," aimed at encouraging more wealthy young Americans to follow the lead of Benz.

"In many American families, money is more taboo than Sex," argues the pamphlet. "Breaking the awkward silence surrounding money is what 'Robin Hood Was Right' is about. We're living a time when many progressive people with money are coming out of the woodwork and starting to act on their beliefs."