Business Notes

AUTOS Idling Away in Motor City

While Wall Street bulls kicked up their heels last week, autoindustry executives in Detroit were grinding their gear teeth in frustration. After an encouraging 1.3% rise in January, domestic sales for the Big Three automakers in the six weeks ending March 10 were 4.7% lower than those in the same period last year. Adding to the less than rosy picture, General Motors announced plans to close five of its plants temporarily to pare an oversupply of slower-selling models, thus idling more than 10,000 workers.

One reason for the auto slump is that customers are not biting very hard at the 9.9% financing currently being offered by U.S. automakers. Japanese auto sales in the U.S., on the other hand, increased 11.5% in February. Detroit may have to offer better deals before its products start moving quickly again. INVENTIONS How to Skin A Copycat

In many offices, workers have used Xerox machines to duplicate confidential documents and pilfer information. Now, though, employers may have a new way of guarding secrets. Norman Gardner, a Toronto entrepreneur, has invented a chemically treated, red-colored paper called Nocopi that cannot be reproduced on a photocopy machine. Nocopi contains a dye that enhances the paper's reflectiveness. When the light shines on the paper inside a copier, the rays bounce back so intensely that the machine's electronic eye cannot "read" the image.

Although Nocopi costs 3-c- to 4-c- a sheet, or about twice the price of ordinary paper, industry experts think that it will be a big seller. Gardner has already sold a large batch to the Ontario legislative assembly. FINANCE Mending a Safety Net

Some 3,000 thrift institutions across the U.S. can assure customers that their deposits of up to $100,000 are insured by the Federal Savings and Loan Insurance Corp. What many customers do not realize is that the FSLIC is running dangerously short of cash. It is run by the Government, but financed by fees charged to insured S and Ls. Though more than 200 savings and loan associations are financially weak and may need up to $16 billion in assistance, the FSLIC has only $6 billion in its coffers.

Last week Edwin Gray, chairman of the Federal Home Loan Bank Board, which regulates the thrift institutions, outlined a long-awaited plan to bolster the industry's insurance fund. In testimony before Congress, Gray proposed that the twelve Federal Home Loan Banks, which are owned by and act as central bankers for the S and Ls, borrow as much as $10 billion from the public by selling bonds. The money raised by these private banks would be used to help replenish the reserves of the FSLIC and give thrift deposits the backing they are supposed to have. GUNS Shot Full Of Holes

Connecticut's so-called Gun Valley, which is home to Colt Firearms and several other weapons manufacturers, was once almost as bustling as California's Silicon Valley. But the gun business has now lost much of its bang. Annual production has dropped by 36% since 1981, to fewer than 4 million handguns, rifles and shotguns. Several companies in Gun Valley have laid off workers, and others, including New Haven-based U.S. Repeating Arms, which took over Winchester's firearms division in 1981, have filed for bankruptcy protection.

The industry has been hurt by tougher gun-control laws in some states and an abundant supply of cheap used firearms. Moreover, many gun enthusiasts are blue-collar manufacturing workers who were laid off in the last recession and have not been rehired. TAXES Poker Is Hard Work

Billy Baxter has been a winner all his life, but he works at it. A professional gambler and a three-time World Series of Poker champion, Baxter earns enough to afford a $1 million home in Las Vegas. But last week Baxter claimed his sweetest pot of all in a Reno courtroom: a $178,000 refund from the Internal Revenue Service.

The case grew out of an earlier IRS ruling that Baxter's $1.2 million gambling winnings for the years 1978 to 1981 were unearned income--in the same category with dividends and interest. Under the tax laws that applied for those years, unearned income was taxable at the maximum rate of 70%. Baxter said the money was earned income, like a salary, which was taxable at a top rate of 50%. In 1984 he filed suit, contending that his winnings were the product of skill and hard work. Last week the U.S. district court in Nevada agreed and ordered the IRS to give a refund with interest. Said Baxter: "Jack Nicklaus gets to file his prize money as earned income. Why not me?"