WASHINGTON (AP) _ The Consumer Product Safety Commission took the first step Thursday toward declaring a chemical widely used in spray paints and paint strippers a hazardous substance.

The commission voted 4-1 to begin a formal rulemaking to declare methylene chloride a hazard, a move denounced by the dissenter as only likely to delay action that should be taken immediately on the chemical, a suspected cancer- causing agent.

Commissioner Stuart M. Statler argued that the agency should immediately declare the chemical a danger, rather than initiate the cumbersome rulemaking, which can take as long as two to three years to complete.

Once the chemical is officially declared a hazard it can be banned or otherwise strictly regulated. Before that can be done, however, the agency must hold hearings, solicit comment from interested individuals and organizations and collect other information on the chemical.

In addition to the safety commission action, the Environmental Protection Agency is reviewing the hazards of the chemical, the Food and Drug Administration has proposed to ban it from hair sprays and the Occupational Safety and Health Administration is working on a program of chronic hazard warning labels for it.

The FDA did conclude, however, that there was not sufficient justification to ban the chemical from use in decaffinating coffee.

''I am prepared to make the judgment that current scientific evidence indicates that (methylene chloride) should be regarded as a hazardous substance,'' Statler said, urging that action be taken promptly.

But other commission members expressed concern that if they acted too quickly, a ban or warning label requirement might be overturned in court, as happened when the agency sought to ban urea formaldehyde foam insulation a few years ago. While studies on animals have indicated the potential cancer- causing danger of methylene chloride, detailed information on its hazards to humans has not been completely documented, according to a commission staff study.

However, in addition to launching the rulemaking, the commission voted 5-0 to direct its staff to work with members of the paint and coating industry to develop warning labels, consumer education programs and other efforts to reduce the danger in the short run.

In addition, industry officials have been working on developing new formulas for their products, using other solvents, and the commission staff was told to assist in that area also.

The paint industry has generally been cooperative, said acting Commission Chairman Carol Dawson.