Edgar Cahn, who exudes ideas as easily as the rest of us exude sweat, is in town today trying to sell his latest brainchild to the D.C. government.

The idea is "service credits," and my advice to the city is: buy it.

Florida already has. The state legislature recently passed Cahn's proposal virtually intact, and as a result, senior citizens in that state are now able to earn the special services they require by doing volunteer work for others. A similar program has been in operation in Missouri since early this year.

The service credits thus generated can be used to purchase respite care ("say you're taking care of an elder relative and you need to get away for a day or two to take care of personal business or just to preserve your sanity") or up to five days a week of homemaker services, including shopping, meals or companion services.

The seniors earn the credits by providing tutorial service, day care, respite care or technical advice, depending on their energy and skill, and draw on them as they are needed. The entire arrangement is computerized, and no money changes hands.

"In theory, private market mechanisms are supposed to supply what people want," says Cahn, a law professor and senior research fellow at the Southeast Florida Center on Aging at Florida International University, Miami. "But the medium of exchange under that theory is money, and elder citizens often don't have it." So he has created a new currency: service credits.

"I looked around and I said 'This is crazy,' genesis of the idea. "We're putting old people on the scrapheap and at the same time, the need for services keeps building up while the money to pay for them is diminishing. Money is supposed to take care of this, but it occurred to me that the real value is not money but service."

And so he came up with his service- credit idea, which he describes as "a mix between the old blood bank idea and a state-operated barter system. Like a blood bank, participants can build up credits against future need; like a barter system, it allows participants to purchase services without cash."

Under the home care/respite care section of the Florida act, only persons aged 60 or older can earn the credits; either that person or a spouse can draw on the credits.

But that is just the beginning, says Cahn, author of the Neighborhood Legal Services Program, a leader in Indian services reform and, with his wife, Jean Camper Cahn, a cofounder of Washington's Antioch School of Law, the first clinical law school for public-interest law.

"The Florida law also provides for experimental programs, which means the idea can expand drastically. You could have members of a congregation earning credits for older members, so they don't have to go into nursing homes. The Little Havana Nutrition Center in Miami is already committed to a program that would have older people run day care centers and tutor young people, with the parents paying for the service by driving or providing other services. . . . Many of Florida's older citizens have their families up north. They don't have the local family ties and the extended family networks, so we have to build the equivalent."

Interest in the idea is spreading. Already, the Southeast Community Hospital Foundation here is doing preliminary computer and market studies to launch the program here.

Eastern Airlines is working out details of a plan that would use its retirees to provide technical advice for mechanics and other service personnel, with the seniors earning access to travel packages. Another program would use retired journeymen to teach young people the skills necessary to render homes and apartments barrier-free.

"When a society has vast unmet needs and at the same time large numbers of talented, energetic potentially productive human beings for whom it has no use, then something is wrong."

Cahn has come up with a brilliant idea for setting it right.