On the eve of a conference at which U.S. senators are expected to question whether the government is doing enough to protect children from TV advertising, a new report issued Thursday is suggesting that the biggest food and restaurant TV advertisers are increasingly directing kids to their unregulated promotional Web sites.

The report from the Kaiser Family Foundation details growing “advergaming,” Web-only spisode and viral marketing targeting children under 13. It comes on the eve of Thursday’s Children’s Now conference, at which senators including Hillary Rodham Clinton, D-N.Y., and Sam Brownback, R-Kan., and three Federal Communications Commission commissioners were slated to talk about the FCC’s role in kids advertising.

Advertisers and media companies are growing increasingly worried about Washington pressure on food and fast-food marketers over the issue of childhood obesity.

Nickelodeon, the target of frequent criticism by critics of junk food marketing, is now running nutrition-related public service ads and announced Thursday it will extend the licensing of characters including Dora the Explorer and SpongeBob SquarePants to three additional fruit and vegetable providers, and also will expand one of its original licenses for additional characters.

The report analyzed current trends in food advertising on the Web, an area with fairly little detailed research to date, and was conducted by Elizabeth Moore, associate professor of marketing at Notre Dame, based on activities last year.

It said that 85 percent of top food brands that target kids through TV also use branded Web sites to market to kids, that 73 percent of the sites use so-called advergames, 65 percent use sweepstakes and promotions, 25 percent use memberships and 53 percent provide online access to TV ads.

In one of the more controversial details, the report said 38 percent of the sites offer kids incentives to purchase products, letting only kids who enter product codes play games or participate in activities or get, at one site, free Nintendo game tips. The report said only 18 percent of sites include information clearly explaining that the site is a form of advertising.

The report said 51 percent of sites contain nutritional information, 35 percent have some educational information and 33 percent have what the report calls “advercation,” or education information directly relating to the product, such as a history of chocolate on Hershey’s site.

Representatives of consumer groups and some critics of kids ads contended the report could provide fuel for further fighting.

Dale Kunkel, a professor of communication at the University of Arizona, told a Kaiser Foundation forum that using viral marketing with kids was an untoward attempt to co-opt kid-to-kid e-mails, essentially “rewarding children for becoming agents of the advertiser.” He questioned whether kids less than 8 years old understand what advertising is and whether they should be the targets of advertising.

Margo Wootan, director of nutrition policy for the Center for Science in the Public Interest, said the problem isn’t the tactics, it’s the foods advertised. She said the ads present “a whole different diet” of foods than those the government advises.

Advertisers and ad group representative said that food Web sites aimed at kids, despite their proliferation, remain a tiny part of the overall marketing mix and characterized the reason for increasing childhood obesity as complex. They also said advertisers are changing what they do, citing efforts by the Children’s Advertising Review Unit to rewrite the ad industry’s rules, consumer demand for healthier products and marketers’ efforts to sell healthier products to kids.

Nancy Daigler, VP of corporate and government affairs for Kraft Foods, said her company, which is now advertising healthier products to kids on TV and radio and in print, is now re-evaluating its Internet sites and expects to make changes to them before year-end.