GERALD P. CARMEN, head of the General Services Administration, has a way to stretch a good deal into a better one: you obtain a low-interest government loan and then you get the government's permission to defer payments. In the past year, Mr. Carmen has been granted two deferrals on $405,000 in outstanding low-interest loans from the federal government. What's more, he notes, "Deferral is available to any American citizen."

Leaving aside who ultimately pays for this government kindness, or exactly who is eligible, Mr. Carmen's approach is an effective alternative to a lot of cold cash on the spot. In 1975, he obtained a $425,000 loan from the Small Business Administration when an urban renewal project forced him to relocate his auto and tire service business in Manchester, N.H. That's a good enough reason, and the rate of interest was good enough, too: 6.5 percent. But having paid $20,000 of the principal, Mr. Carmen hasn't made a monthly payment in 11 months.

An SBA spokesman notes that this is "a normal SBA procedure when a loan client through no fault of his own finds himself in financial difficulty and asks for a deferral. It is not a delinquency." In fact, says this official, 17,000 of 149,750 such loans are currently late by 60 days or more.

So don't worry about it--and never mind that three months before Mr. Carmen stopped paying off his loan, President Reagan ordered a crackdown on those owing the government for loans and back taxes. After all, the president might not even have known about this case anyway--since Mr. Carmen failed to list the loan as a liability on his financial disclosure statements. He says he would have listed it if he had thought it was required. Again, so what if the instructions require a listing of any business liability "in which your participation or ownership interest extends to personal liability for its debts."

This last point is prompting a few inquiries from the Office of Government Ethics. It should. But otherwise, Mr. Carmen is merely a role model for anyone who is in need of some kindness from the federal government. If things get a little tight, one need only look up to the head of the GSA for a guideline on how to make payments to the government: better late than on time.