The Senate Finance Committee, which happily has bestowed tax breaks on oil, timber and citrus fruit, yesterday tightened the cummerbund on tuxedos.

It all began when Sen. John Heinz (R-Pa.) tried to do a favor for the rental-tuxedo industry. He suggested that formal-wear rental firms be allowed to write off the cost of their garments over three years rather than the current five, so that customers wouldn't have to wear threadbare five-year-old tuxedos.

"They just don't last that long," Heinz said.

But Sen. Daniel Patrick Moynihan (D-N.Y.), hemming and hawing, pointed to Deputy Treasury Secretary Richard G. Darman, and observed: "I've seen Mr. Darman in a tuxedo that was clearly more than five years old."

Right, Darman responded. He owns the tuxedo, which he admitted was as bedraggled as Moynihan claimed. It is 17 years old.

Seeking to iron out the objections, Heinz noted that the tax bill being considered by the committee would let automobiles -- presumably more durable than clothing -- be written off over three years. Surely senators could do the same for tuxedos.

Committee Chairman Bob Packwood (R-Ore.), whose own tuxedo also is 17 years old, worried such a move would cause an image problem. "There are some things we do to make ourselves look foolish and some things we do to make ourselves look really foolish," he said.

The chairman wouldn't say that if he were a haberdasher, like the late president Harry S. Truman, Heinz sniped.

"Yes, and he went bankrupt," Packwood said. "Maybe because he didn't have three-year depreciation."

The amendment was defeated, 6 to 5.