The two Soviet spacecraft that landed on Venus last month apparently sent back no pictures and almost no information on the planet's surface.

Western space sources said they do not know if the cameras and instruments on board the two Soviet Landers failed, or if the radio link failed between them and the relay spacecraft that flew by Venus at the same time they landed. One landed Dec. 21, the other on Christmas Day.

Both landers were equipped with panoramic cameras, a shovel to test the mechanical properties of the soil of Venus and an X-ray fluorescent spectrometer to analyze the radioactivity in the rock. A passive instruement, the X-ray device was built to tell Soiets scientists how much of the planet's intense surface heat was due to the radioactive decay of such minerals as uranium, thorium and an isotope of potassium.

This was the first time the Soviets flew either the shovel or the X-ray instrument to Venus. The Soviets told their American counterparts about the two instruments at a meeting last fall in Austria and then asked the Americans not to disclose this information publicly until after the Soviet Venus mission was over.

The Soviets said their first lander, Venus 12, had yielded a "rich harvest" of information about the planet, but they never disclosed what the lander had found. The Soviets said little about their second vehicle, except that it landed safely on the surface.

The first lander transmitted information for two hours three days after it landed, the Soviets said. Then it went dead. Scientists assumed the surface heat of almost 900 degrees Fahrenheit killed its communications.

Western scientists said they believe the "rich harvest" the Soviets talked about referred to the information the first lander gathered from the atmosphere of Venus on its way down to the surface. These scientists do not believe the Soviets were trying to be misleading about what the landers found after they landed.

The two Soviet spacecraft landed on Venus three weeks after four American probes fell through the thick clouds to the surface of Venus. None of the American spacecraft was built to land, although one survived and kept sending signals back to Earth for more than an hour after it struck the surface.

Ironically, the National Academy of Sciences has recommended that the United States undertake a joint mission with the Soviet Union to land a spacecraft on Venus to dig up soil and do a robot analysis of it. One reason the academy recommended such a joint mission was previous Soviet success in landing spacecraft on Venus.