Some of America's leanest manufacturers share a fat secret.

Companies like Whirlpool and Caterpillar are making costly additions to their otherwise sinewy supply chains to compensate for aging U.S. roads that are too potholed and congested for "just in time" delivery.

Some opt to keep more trucks and inventory on the road. Others are leasing huge "just in case" warehouses and guarded parking lots on the edges of big cities. All that activity raises costs, which are expected to increase even more if roads are allowed to deteriorate further and an improving economy boosts traffic.

Of all the holidays on the American calendar, Labor Day is the only one whose origins have what might be called a socially didactic quality. The parades, the speeches, the day of rest, were all initially aimed at sending messages about the class struggle. The grand marshal of the first Labor Day celebration, held in New York City in 1882, has been quoted as saying, ''Let us offer monopolists and their tools of both political parties such a sight as will make them think more profoundly than they have ever thought before.''

According to Ellen M. Litwicki, author of ''America's Public Holidays,'' that first Labor Day was an utterly different kind of holiday than the one we know now, which has little to do with profound thinking of any kind by monopolists, their political tools, or even ordinary workers. Following a mammoth parade, New Yorkers in 1882 crowded into a park where, after much speech-making, they ''ate their lunches, drank beer, listened to German singing societies and Irish fiddlers, danced to union bands, and viewed fireworks displays in the evening.'' It sounds like the Fourth of July, with a touch of St. Patrick's Day and May Day thrown in.