ON THE FIRST of the month, a new law of great importance to the divorced and widowed went into effect. Passed as part of the massive budget reconciliation act in April, it didn't receive much attention. But it will provide badly needed protection to those who would otherwise lose group health insurance coverage because of a change in work or family status.

Most Americans who have private health insurance are covered by group plans at work. When they lose their jobs, they lose this protection, usually immediately. The death or divorce of the covered worker also means that his family is no longer protected by his insurance. The new law is intended to alleviate these hardships by requiring employers to continue to provide coverage for a specified period of time for five groups of people. Widows, divorcees and spouses of retiring workers and their dependent children can obtain coverage for three years. Unemployed workers and their dependents can retain insurance for 18 months. And children of covered workers can continue coverage for as long as three years after losing dependent's eligibility because of age.

The new law does not apply to those who have already lost health insurance, and it is not binding on small employers or state and local governments. It requires beneficiaries to pay full monthly premiums -- both the employer and employee portions plus a 2 percent fee for administrative costs.

Divorced women with dependent children, and older women, both widowed and divorced, constitute a high percentage of the American poor. Most of them lost an extremely important asset when their spouses left or died. For a large number, individual health insurance policies are either prohibitively expensive or simply unavailable because of age or personal health problems. In the future, this new law will offer at least temporary protection for women in these circumstances and for others whose change of status would otherwise leave them without health insurance coverage.