By CHERYL JENSEN

olvo, the pioneer of the lap-and- shoulder safety belt now in common use, has begun to ask: If three is good, can four be better?

The widely used belt, called a three-point belt because it is anchored on both sides of the hips and behind one shoulder, is considered the most effective safety feature available. But safety researchers at Volvo and its parent, Ford Motor , say an even better device may be available: a four-point belt akin to those used in racecars, with an extra shoulder strap. They are looking at two versions and conducting crash tests.

The first type, called V4, has shoulder straps much like those of a child safety seat. The upper attachment points are in the seatback near the shoulders. A person pulls the straps over each shoulder and fastens them to a buckle in the middle of a lap belt.

The other belt, the X4, adds another shoulder belt to the conventional three-point belt. The three-point belt is put on first, by pulling it across the chest and buckling it as usual by the hip. The additional belt crisscrosses the chest and is buckled on the opposite side.

Researchers say that the extra belt holds a person in the seat if a vehicle rolls over or is hit from the side. They also expect it to distribute crash forces more uniformly over the chest, reducing the pressure by half.

In addition to crash tests, the companies are evaluating the comfort and convenience of the four-point belts in customer clinics to see which design people prefer, and why.

Volvo introduced its three-point belt in 1959 in the front seats of cars sold in Scandinavia. The company brought the belts to the United States in 1963, and the federal government began to require three-point belts in 1968. The agency estimates that the devices saved 123,213 lives from 1975 through 1999. Belt use reached a record high of 71 percent last year.

Safety engineers are asking two questions about three-point belts, which have changed little since their introduction: Could they be made even safer? Could they be more comfortable so more people would wear them? A survey of 5,000 consumers, aimed at getting statistically valid results, may provide answers and help to determine whether four-point belts have a place in future cars.