Minors trying to buy cigarettes have a 2-out-of-3 chance of succeeding, according to an undercover operation that tested one state's law against selling cigarettes to people under age 18.

Federal health oficials reported Thursday that Colorado's 1987 law prohibiting merchants from selling tobacco to minors and prohibiting youngsters from buying wasn't working too well.The national Centers for Disease Control said many vendors may not be familiar with this law, and "some may believe enforcement is unlikely or that the profits from cigarette sales to minors outweigh possible financial penalties for violating the law."

The fine for violations, by merchants or juveniles, is only $25, said Walter Young, director of the Prevention Programs division of the Colorado Department of Health.

The Coalition for a Tobacco-Free Colorado, a consortium of public and private health organizations, sent 11 young volunteer teams to 121 sites to see if the children could buy tobacco. At 77 sites, or 64 percent, they were successful.

"It's disappointing that merchants have not gotten the message that they're not supposed to sell to kids," Young said.

All 24 times that minor volunteers went to a cigarette machine, no one stopped them. The 97 other attempts involved vendors or sales clerks; 53 of those were successful.

Colorado's cigarette snoops ranged from age 9 to 17. The survey was done in August 1989.

"Sales clerks did not appear to discriminate in their sales practices between very young adolescents and those closer to legal age," the CDC said.

Among those buying from sales clerks, the success rate for volunteers ages 15-17 was 55 percent, virtually identical to the 54 percent success rate for the other volunteers.

Options that could cut down on illegal cigarette sales include banning cigarette machines, but machines account for less than 10 percent of sales to minors, Young noted.

The CDC said that the minors participating in the project didn't actually break the law. They approached machines but didn't buy, and they told any helpful clerks they didn't have enough money for the purchase.