They're only talking about saving pennies, but principle means something, so some 5,800 Maryland tobacco farmers are voting next week on whether they want to pay for a federal service many of them don't think they need.

The Agriculture Department is conducting a referendum by mail to determine whether the tobacco farmers want to continue to have their leaf graded by federal inspectors--and, for the first time, pay for it.

Larry L. Crabtree, an official with USDA's tobacco division, said that if the farmers vote against continuing the grading service, the Maryland tobacco marketing season will open without federal graders for the first time since 1935.

Under the federal tobacco price-support program, grading is important. It helps determine how much support the government will pay for a given grade of tobacco if it isn't sold at auction.

Marylanders voted to leave the price-support program in 1965, which, in effect, made the grading service unnecessary. But the service was free and nobody complained when it continued. Since 1965, they've been selling their prized Type 32 broadleaf, a cigarette ingredient, with no trouble, at increasingly better prices.

Prodded by the Reagan administration, Congress last year decided to impose fees for certain federal services--among them, tobacco grading. For Marylanders, who last year grew 28.7 million pounds of tobacco, the fee would be 45 cents per 100 pounds--or a total of about $129,500 for the Maryland industry.

"For an individual farmer, it's not a lot of money," said W. A. Gallahan III, a tobacco grower in Prince George's County. "It's more the principle of the thing. Why pay for it if you don't need it?"

Maybe Congress did tobacco growers no big favor by imposing the fee. But at the insistence of Rep. Marjorie S. Holt (R-Md.), it gave Maryland farmers a little advantage in last year's farm bill.

Farmers who produce flue-cured and burley tobacco in other states can no longer grow Maryland-type tobacco without having it count against their burley and flue-cured growing quotas. That's expected to mean that more Maryland farmers will grow more Maryland tobacco--and make more money.