The United States should undertake a space mission to dig up a sample of Mars and return it to Earth at the same time that it undertakes a joint mission with the Soviet Union to perform a robot chemical analyis of the soil on Venus.

These are the two major recommendations of the National Research Council, the study arm of the prestigious National Academy of Sciences. Its Committee on Planetary Exploration, in a report scheduled for release today, has strongly suggested that the United States in the next 10 years redirect its attention to Mars and Venus, the two sister planets of Earth that are similar to and different from Earth.

"The Earth, Venus and Mars are as close as you're going to get to triplets," said Dr. Gerald J. Wasserburg of the California Institute of Technology, who is chairman of the committee making the recommendations. "If you want to understant what gassy, rocky planets are like the real analogues are these three planets."

In recommending that the United States turn its sttention once more to the inner planets, the Committee on Planetary Exploration pointed out that its goal of four years ago for exploring the outer planets is already underway. Two Voyager spacecraft will reach Jupiter this year, a Pioneer is approaching Saturn and one of the two Voyagers will continue to Uranus after its exploration of Jupiter.

Uppermeost in the committee's mind is a plan to land on Mars a robot spacecraft to dig up at least one sample and return it to Earth. Cost of such a mission would be between $1.5 billion and $3 billion and would be spread over 10 years.

By returning a Martian sample to Earth, scientists could pinpoint the time in geologic history when almost every major event took place on Mars. They could identify the origins of the giant Martian volcanoes and canyons whose size appear to be unrivalled anywhere in the solar system. They could tell when water disappeared from the surface of Mars and where it went.

"Mars is closely linked to the Earth by virtue of the volcanic, erosional and climatic phenomena it is known to exhibit," the committee report said. "The study of Mars is an essential basis for the understanding of the evolution of the Earth."

In steppig up the exploration of Venus over the next 10 years, the committee recommended two missions to our nearest planetary neighbor. The first would be the orbiting of a huge radar dish to get a global map of the hidden surface of Venus, the' second the landing of a spacecraft to conduct a robot chemical analysis of what is believed to be the most complex and radioactive soil in the solar system.

The committee strongly recommended that the United States begin talks to undertake this mission jointly with the Soviet Union, in part to share the costs, and in part because the Soviets have done their most aggressive exploration of the planets at, and on, Venus.

"It is the view of this committee that continued scientific exploration of Venus offers an ideal arena for cooperation between the Soviet Union and the U.S.," the report said. "We recommend that a first collaboration proceed through the independent development of complementary experiments to be flown on a single spacecraft and plan for an early collaborative launch."