WASHINGTON - (AP) - Federal regulators will require sunscreenmanufacturers to test their products' effectiveness against sunrays that pose the greatest risk of skin cancer. Under new rulesbeing announced Tuesday, they also will have to follow stricterguidelines when describing how well their products work againstultraviolet B rays.

Currently, the Food and Drug Administration only requirestesting for ultraviolet B rays that cause sunburn. That's what thefamiliar SPF measure is based on.

Starting by next summer, products must be tested for how wellthey deflect the more dangerous ultraviolet A rays. UVA rays aremost commonly linked to skin cancer.

The federal government first announced plans for sunscreenstandards in 1978. The process was delayed by difficultiesassessing UVA protection.