NEW YORK (AP) _ Makers of the new heartburn drug Pepcid AC have fired a counter shot in their war with arch-rival Tagamet HB over each other's advertising.

Johnson & Johnson-Merck Consumer Pharmaceuticals Co. said Wednesday it has sued SmithKline Beecham PLC in federal court in New York, charging that SmithKline's ads for Tagamet make false claims about Pepcid's speed and doctors' preferences for the two drugs.

Those are among the same issues in a suit filed a week ago by SmithKline against J&J-Merck.

Pepcid AC and Tagamet HB are locked in a marketing fight for a piece of the $1 billion-a-year antacid market.

The two drugs _ well-known as prescription medicines for ulcers _ were introduced this year in non-prescription form as a new long-lasting class of antacid.

Each drugmaker is spending an estimated $100 million in saturation ads on network television and national magazines. Their ads make similar claims and counter claims as their suits.

J&J-Merck ads and its suit say Pepcid provides heartburn relief in 30 minutes or less. They also say the drug controls acid for nine hours, while admitting that actual relief of symptoms may be somewhat shorter.

SmithKline ads and its suit say Pepcid takes at least an hour to start working, making its nine-hour claim of acid control false.

Each company also claims doctors prefer its product. The suits challenge the validity of each other's methodology.

Tagamet ads say doctors prefer it 7-1 based on the total number of prescriptions written for the two drugs. J&J-Merck's suit says that's irrelevant because Tagamet's prescription form was introduced in 1977 and Pepcid's didn't arrive until 1983.

J&J-Merck paid for a survey of 800 doctors and pharmacists regarding the two drugs. It showed showed eight out of 10 prefer Pepcid over Tagamet.

Both lawsuits demand a court injunction against each other's ads, corrective advertising, and unspecified punitive damages.