WASHINGTON — Two safety groups are stepping up their campaign for an expansion of the Firestone tire recall to include the 16-inch size of the ATX, ATX II and Wilderness A/T tires.

Public Citizen and Safetyforum.com have scheduled a news conference for 1.00 p.m. Monday to announce formation of a concerned Firestone tire owners group.

Firestone and Ford Motor Co. (F.N) announced last week the recall of 6.5 million of the 15-inch versions of the tires in response to a government probe of accidents linked to 46 deaths that involved peeling of tread from the tires.

A majority of the tires were fitted to Ford Explorer sport utility vehicles as standard equipment.

Safety advocates have questioned why Ford offered to replace 16-inch tires on vehicles overseas but not in the United States.

The companies have limited the recall to all 15-inch ATX and ATX II tires, and those Wilderness tires made at Firestone's Decatur, Ill., plant, assuring consumers they have narrowed the problem to these tires.

The recall will also occur in phases, starting with four large southern states, then moving to remaining southern states before tackling the rest of the country. Highway driving in hot weather seems to be a factor in the problem.

The northward-creeping recall has drawn complaints from vehicle owners and some state attorneys general. A Public Citizen official said consumers from Maryland and Canada would describe their problems with the tires at the news conference.

Firestone, owned by Japanese tiremaker Bridgestone Corp (5108.T). , made 14.4 million of the 15-inch tires subject to the recall but only 6.5 million are thought to still be in service.

By either count it is the second-largest tire recall in U.S. history since Firestone recalled 14.5 million of its 500 series