WASHINGTON, Feb 3 (Reuters) - U.S. health officials are worried that flavored, dissolvable tobacco products can look too much like candy and are probing companies for more information to weigh the risk of nicotine addiction and poisoning in children.

The U.S. Food and Drug Administration has sent letters to Reynolds American Inc's R.J. Reynolds Tobacco Co and Star Scientific Inc seeking details on their marketing practices, use in younger consumers and incidents of possible overdose.

Any move by the FDA to further regulate or even remove dissolvable tobacco products from the U.S. market would be a blow to Star Scientific. The one-time cigarette manufacturer has shifted its focus to making products it says expose consumers to lower levels of toxins.

The tobacco industry overall is increasingly looking toward products to replace traditional cigarettes, as smoking's stigma and U.S. bans on smoking in public grow.

R.J. Reynolds Tobacco Co and Star Scientific " which have been embroiled in a patent dispute over some of the technology behind the dissolvable products " sell products containing powdered "smokeless" tobacco that can be brightly colored with flavors such as coffee and mint.

Companies have argued such alternatives are aimed at adults who cannot light up in public or as a step for those looking to stop smoking. While laws vary among U.S. states, most limit tobacco product purchases to those 18 and older.

The FDA, in the Feb. 1 letters released late Tuesday, expressed concern the products could lure children and teenagers. Use of the products could entice children at younger ages, lead to nicotine addiction and cause "inadvertent toxicity.".

The FDA is "concerned that children and adolescents may find dissolvable tobacco products particularly appealing, given the brightly colored packaging, candy-like appearance and easily concealable size of many of these products," wrote Lawrence Deyton, head of the FDA's Center for Tobacco Products.

A public meeting on tobacco issues will be held later this year by the FDA. Agency officials have quickly moved to exercise their new oversight of tobacco products after a law granted them the power last year.

Sara Troy Machir, a spokeswoman for Star Scientific, said the company was not surprised by the letter and would cooperate fully. "We're happy to share information with them," Machir said, adding that Star's smokeless products " Ariva and Stonewall " have been on the market for 10 years.

R.J. Reynolds markets three types of similar products under its Camel brand that deliver dissolvable nicotine in tablet, mouth strip and small matchstick-like forms.

Spokesman David Howard said R.J. Reynolds was reviewing the FDA's request and would respond within the two-month deadline set by the agency.

Campaign for Tobacco-Free Kids President Matthew Myers, whose advocacy group backed the law granting FDA authority over tobacco products, said the letters showed the agency "intends to act aggressively" to regulate the controversial industry.

Shares of Star Scientific closed down 1.8 percent on Wednesday, while shares of R.J. Reynold's parent company closed up 0.3 percent.

The FDA posted the letters on its website at http: www.fda.gov/TobaccoProducts/GuidanceComplianceRegulatoryInformation/default.htm.