Minnesota's powerful anti-smoking lobby is again backing legislation that would ban tobacco advertising on billboards, which would make it the only state beside Utah to outlaw such advertising.

But opponents say a federal pre-emption over state laws on tobacco product ads and promotions, which took effect when warning labels were added to cigarette packages and ads in 1965, would make any state ban invalid."It's very clear. I don't know how you get around that," said Jim Erickson, a lobbyist for the Minnesota Outdoor Advertising Association, which opposes the bill.

"It depends to some extent on what the arguments given for the bill are," countered Northeastern University law professor Richard Day-nard, chairman of the Tobacco Products Liability Project.

"What is pre-empted are only those prohibitions or restrictions on advertising or promotion based on smoking and health," said Daynard.

But if the bill is based on discouraging minors from smoking, that's a different matter, say Daynard and other supporters.

Despite the arguments, Utah's law banning billboard advertising of tobacco products - believed to be the only state prohibition of that kind - has not been challenged in light of the federal pre-emption.