Outward bound from Jupiter, Voyager 2 dramatically confirmed today that the giant planet is circled by enormous ring invisible from earth but dazzling when viewed behind the planet looking back toward the sun.

In a beautiful sequence of photographs, the ring stands out in brilliant clarity around Jupiter, which is blocking the sun from the view of the spacecraft so its cameras get the best photographs of the ring.

"We were amazed that the ring showed up as bright as it did," the University of Arizona's Dr. Bradford Smith said today at the Jet Propulsion Laboratory where Voyager is directed, "but there's no question that it's there and it's been there all along."

First found by voyager 1 in March but photographed then as a faint, broken circle, the ring around Jupiter stood out today as clearly as Saturn's rings do in Earth-based telescopes. Smith said the ring is six-tenths of a mile thick, 4,000 miles wide and makes a perfect circle 81,000 miles out from the palnet.

Smith described the ring as containing billions of fine particles which he said makes it hard to explain its stability and even harder to explain its permanence. Clearly visible in the photographs of the ring are clouds of particles being pulled out of the ring and into Jupiter by its enormous gravitational force.

"Why doesn't Jupiter swallow it up?" Smith asked. "We have no idea."

Smith said the ring is invisible from Earth because of the fineness of its particles. In fact, the Pionerr II spacecraft that flew by Jupiter five years ago went through the ring without detecting it. The dust is so fine that it does not reflect light, it only scatters light forward.

"Imagine the hair of a woman back-lit by the sun and the way the finest hairs stand out in the light," Smith said, "and you might understand what I mean."

Scientists believe the ring around Jupiter is primordial debris that would have formed a moon if the tidal forces of Jupiter had not been so strong. Scientists do not believe it is anything like the rings of Saturn, which are believed to be a mix of ice and large boulders.

"The radiation around Jupiter would have sputtered away any ice pretty fast," Dr. Laurance A. Soderblom of the U.S. Geological Survey said. "And the way the light scatters, there are just not any large boulders."

Besides views of the ring.Voyager 2 also returned to Earth today its best pictures of the large moon Ganymede, which it had taken two days ago and stored on its video tape racorder. Groove after groove stood out on the moon's rich brown surface. Soderblom believes they are ridges of ice that thrust up from cracks in the somewhat fragile crust of Ganymede.

Visible in one picture was a 140-mile-wide crater whose white rays extended 2,000 miles in every direction. Soderblom called it "one of the most spectacular craters" in the solar system.

"The relatively small meteorite that produced that crater has damaged the crust and produced fresh snow from below the crust," he explained. "It's polarized that ice just like a somebody hitting a windshield with a hammer."

Fresh photographs of the moon Europa show what Soderbolm calls the "flattest surface in the solar system." The pictures show no relief, no mountains, no ridges, no hills, no valleys and no craters.

"We believe the surface of Europa is made up mostly of very soft ice," Soderblom explained, "which moves and covers over every piece of topography it has. CAPTION: Picture, Voyager 2, looking back toward sun, catches unexpectedly bright ring of Jupiter. AP