A consumer group yesterday urged the Federal Trade Commission to require that all aspirin advertisements include warnings that the drug is "strongly linked" to the sometimes fatal Reye's Syndrome in children treated for flu or chicken pox.

In a letter to FTC Chairman James C. Miller III, the Public Citizen Health Research Group, founded by Ralph Nader, asked that the agency require the warning under its authority to prohibit unfair or deceptive advertising for over-the-counter products.

A spokesman for Miller, Susan Ticknor, said the commission had not yet received the request, but "we do have measures we can take to act quickly" if the situation is an emergency.

The consumer group cited a new Centers for Disease Control pilot study, released last week, that said children given aspirin for chicken pox or flu had a 25 times greater chance of developing Reye's Syndrome than children not given aspirin.

Health and Human Services Secretary Margaret M. Heckler cited the study in asking aspirin makers to put warning labels on their products, pending a final study to be completed by the end of 1986.

Aspirin makers have agreed to develop labels, and are meeting with Food and Drug Administration officials to work out the wording.

But Public Citizen wrote Miller that even if labels are changed, the industry's print, television and radio commercials "currently mislead parents into believing that there is no danger in giving aspirin-containing medications to their children who have chicken pox, flu or flu-like symptoms."