Upholstered furniture will be more fire-resistant after July 1 when many manufacturers begin using new safer materials and techniques approved by the industry and government, the staff of the Consumer Product Safety Commission reported yesterday.

But there is one catch--the safer chairs and sofas won't appear to be different from those made with more hazardous materials, said James Hoebel, manager of CPSC's fire hazards program.

"The changes aren't visible because they are on the inside of the cushions," Hoebel said. "And there are no plans at present for the label to explain that the changes have been made."

However, at the request of Commissioner Sam Zagoria, Hoebel agreed to ask manufacturers to consider adding label information that would inform buyers of the improvements.

The fire safety changes to be made on a voluntary basis by manufacturers include the addition of a heat-conducting welt cord and a fire resistant synthetic interior fabric between the cushioning material and outer fabric.

Not all upholstered furniture will incorporate the safety improvements, however. An estimated 25 percent of all sofas sold don't have welt cording and therefore can't utilize the new heat-conducting welt protection.

Manufacturers don't have to adopt the fire safety innovations, which are part of the voluntary program sponsored by the Upholstered Furniture Action Council, a trade association. Furniture made by UFAC members accounts for about 85 percent of the U.S. market and bears a gold tag saying "UFAC" and "Important Consumer Information."

During 1981, there were 39,000 upholstered furniture fires resulting in 1,400 deaths, according to CPSC statistics. Of that, 24,600 fires and 1,150 deaths were caused by cigarette ignitions.

Prior to the initiation of the UFAC program in 1979, "almost all upholstered furniture was susceptible to ignition," Hoebel said. But since then UFAC has concentrated on increasing the use of synthetic fibers and decreasing the cellulosic fibers, such as cotton and rayon, he said. Another important step was to increase the use of treated flame-retardant cotton batting, he said.