The cause of an April 6 fire that killed a 53-year-old woman on A Street SE was "careless smoking;" according to the D.C. Fire Department. Smoldering cigarettes also caused a fire that killed twin boys, aged 3, on Sixth Street NW on Feb. 25.

Those cases are evidence of the need for the U.S. Cigarette Safety Act, which was approved by Congress on Oct. 4.

"With the sole exception of air bags or passive restraints in autos, there is no other single measure . . . more likely to save more lives each year than the introduction of a fire-safe cigarette," said Consumer Product Safety Commissioner Stuart M. Statler.

The act authorizes a feasibility study of regulations requiring that cigarettes be made to extinguish themselves quickly if they have been left to smolder.

The problem, Statler said, is that cigarettes are designed to remain lit for long periods when unpuffed.

A result is that cigarettes cause 35 percent of all home fire fatalities. The most recent national statistics available show that, in 1982, cigarettes and other smoking materials caused 56,400 residential fires, and 1,730 deaths.

Advocates of fire-safe cigarettes believe that the new legislation is the first step toward reducing cigarette-caused fires. The advocates include a broad coalition of consumer, fire service and medical organizations that has worked closely with sponsors of the legislation, Rep. Joe Moakley (D-Mass.) and Sens. Alan Cranston (D-Calif.) and John Heinz (R-Pa.).

But efforts to enact a cigarette safety proposal have been blocked by the tobacco industry until this year, when the two sides reached a compromise.

Under the terms of the law, which President Reagan is expected to sign shortly, a feasibility study will be directed by a committee of three people: the chairman of the CPSC, the U.S. Fire Administrator and the assistant secretary of health of the Department of Health and Human Services.

Working with that committee will be a 15-member technical group that will include representatives from public health, fire safety, furniture and tobacco industries.

Commissioner Statler said some possibilities may include:

Causing the tobacco to burn faster to reduce the time of contact with a flammable surface and possibly cause the cigarette to extinguish quickly if left unpuffed.

Packing cigarette tobacco loosely, to make it burn faster, or tighter to burn out quicker.

Adjusting the amount or blend of tobacco to cut down on available "fuel."

Removing chemicals (citrates) from the paper that cause it to burn evenly with the tobacco, or adding chemicals such as sodium silicate to promote self-extinguishment.

Changing the type of cigarette paper altogether, making it more dense so that it won't burn so hot, or more porous so it burns down soon.

"The technology to produce a fire-safe cigarette -- one with less propensity to ignite furniture and bedding -- is within our grasp," Statler said. "And with this legislation, work too long postponed may now begin immediately to come up with a cigarette that simply burns less long or less intensely."