As of January 1 of next year, all automobile passengers in the state must wear seat belts as a result of a bill signed into law yesterday by Gov. Michael S. Dukakis.

The ruling, which is the only one of its kind in the country to require both front and back seat passengers to wear belts, will impose a $15 fine on each violator.

Massachusetts is the 16th state in the country to institute such a law.

Police officers will be allowed to issue violations only after they have pulled over a car for a separate moving violation, said Jeffrey Grossman, a spokesman for the Massachusetts Executive Office of Public Safety, a primary supporter of the bill

Police officers, mailmen, and certain operators of delivery vehicles will be exempt from the law. But firefighters and taxicabs will be subject, and taxis will forced to install seat belts, said Grossman.

Squeaked By

The bill--which passed by the slim margin of 77 to 62 in the State Assembly on October 16--was opposed by a number of legislators who called it a violation of citizens' rights. Proponents argued that the requirement is a public health measure, and that the Supreme Court has ruled that driving is a privilege rather than a right.

Many states have begun mandating seat belt use since New York was the first state to do so last January. The bill's supporters argued that New York's law was successful, decreasing highway fatalities by 27 percent in its first three months on the books.

House Rep Thomas P. White (D-Worcester) and State Senator William Keating (D-Sharon) authored the bill. But House Rep. Frank Woodward (D-Walpole) was one of the bill's staunchest supporters. Woodward's 18-year-old daughter died in a car accident when her vehicle was hit by a drunk driver. His speech, in which he said she would have survived had she been wearing a seat belt, brought the house to its feet and won support for the bill from many legislators, Grossman said.