I didn't think it was much of an idea when the Rev. Leon Sullivan proposed it several months back. President Reagan, in his Thursday news conference, proposed it again. It still isn't much of an idea.

What Rev. Sullivan, head of the Opportunities Industrialization Centers, proposed, and what the president echoed, was an approach for dealing with this country's joblessness: old- fashioned neighborliness.

"If a lot of businesses would take a look and see if they could hire just one person, it would be interesting to see how much we could reduce those employment rolls," the president mused. "If everyone would just simply look at it from the standpoint (that) there are more businesses in the United States than there are unemployed. . . ."

Approximately 12 million Americans are out of work. There are, according to the Census Bureau, approximately 14.7 million businesses. If they would each do what Reagan proposed, we'd have a quick end to unemployment.

It's an idea that is intriguing for the first 10 seconds you think about it. Presidential counselor Ed Meese thought about it for 10 seconds and, in post-news coference remarks, started to explain it away. "This may really involve in some cases not letting someone go that they might have to, by staggering work hours or something like that," Meese offered. "That's what the president is talking about."

That isn't what the president was talking about. He was talking about "the neighborly spirit in America . . . so personally gratifying to every one of us all across the country" and reflecting on the fact that, since there are more businesses than people officially seeking work, this gratifying neighborliness could solve a major problem.

Reagan himself recognized that his proposal wasn't quite perfect. Some businesses, "because of their own troubles," wouldn't be able to put on one additional person, but, on the other hand, some might be able to hire more than one, so. . .

The major flaw in that line of thinking becomes obvious when you look at the nature of those 14.7 million businesses. Most of them-- 11.3 million, according to the Census Bureau's latest figures--are "proprietorships": mom- and-pop stores, service operations in which employer and employee may be the same hard- pressed person, tiny concerns with little or no payroll.

Not only are these businesses unlikely to respond to the president's off-the-cuff proposal or Meese's modification of it; many of them are struggling to keep afloat. Indeed record numbers of them are going under, with bankruptcies at a post-Depression high.

One suspects that Reagan, with his love for the simple American virtues, is imagining a situation different from the one that actually exists. When the overall economy was in better shape, there were towns and states that undertook campaigns to make jobs available to the Asian "boat people." There were employers who, responding to calls for civic sacrifice, created summer jobs for needy youths. But, commendable as these efforts may have been, they had negligble effect on overall jobless rates.

I know the president doesn't think much of federally sponsored "make-work" projects, but if the immediate problem of unemployment is to be addressed, the government is going to have take a hand in it. Yuletide appeals to neighborliness won't do it, nor will presidential phone calls on behalf of heroes who rescue strangers from subway tracks.

Let's see, there are 12 million people out of work, and if we have X number of miles of subway lines . . .