WASHINGTON – The government is pressuring food companies to cut back on marketing unhealthy foods to children, releasing guidelines Thursday that could phase out advertisements on television, in stores and on the Internet if companies agree to go along with them.

Under the voluntary guidelines, companies would be urged to only market foods to children ages 2 through 17 if they are low in fats, sugars and sodium and contain specified healthy ingredients. The proposal sets parameters that are stricter than many companies have set for themselves.

If companies agree, children could see much less of the colorful cartoon characters used to advertise cereals or other gimmicks designed to draw their attention.

It is unclear whether government pressure will be effective enough to get many companies to sign on. Some of the country’s largest food companies, including McDonalds, General Mills Inc., Kellogg Co., Kraft Foods Global and PepsiCo Inc., already have joined an initiative sponsored by the Better Business Bureau to limit their marketing to children. The standards are similar but not as strict as the government proposal.

Through similar initiatives and as a result of public pressure, the industry has been successful in reducing the number of television ads aimed at children in recent years, although much of that advertising has moved to the Internet, social media and other digital platforms such as smart phones. Public health advocates have argued that the industry’s self-regulation is not enough and pushed the government to set guidelines to pressure them.

In 2009, Congress directed the Federal Trade Commission, Agriculture Department, Food and Drug Administration and the federal Centers for Disease Control and Prevention to form a working group and develop the recommendations. The guidelines they wrote are broad, applying to digital media and almost any promotion a child might see for a food, including text messages, product placement in video games and celebrity endorsements.

The agencies said the proposal, which would be phased in over five years and is up for public comment until the summer, is “to encourage a marketing environment that supports, rather than undermines,” parents’ efforts to get children to eat healthy food.

The effort is one of many Obama administration initiatives aimed at combating childhood obesity. First lady Michelle Obama has pushed for better school lunches, healthier restaurant meals, more physical activity and other healthy lifestyle changes as part of her “Let’s Move” campaign.

Specifically, the marketing guidelines recommend that companies market only foods that have a significant amount of fruits, vegetables, whole grains, low-fat milk products, fish, extra lean meat, eggs, nuts, seeds or beans.

Foods that contain more than a certain amount of trans-fat, saturated fat, added sugars or sodium per serving would not be eligible for marketing to children.

The proposals suggest the industry focus its efforts on foods that are most heavily marketed to children, including breakfast cereals, carbonated beverages, restaurant foods and snack foods.