Despite serious uncertainties about funding, NASA yesterday announced that McDonnell Douglas Astronautics and Boeing Aerospace have won multibillion-dollar contracts to design and build a space station in which eight astronauts would live and work for six months at a stretch.

The 320-ton space station, which is expected to cost $14.6 billion to $23 billion or more, would orbit 250 miles above Earth and contain four modules in which the astronauts would live and conduct research. The station could later become a staging platform to launch flights to the Moon or Mars.

The contract awards, considered the biggest plum in civilian space for the next decade, boosted the manned station closer to reality. But as Congress struggles in coming weeks to lower the federal deficit, the National Aeronautics and Space Administration and the winning companies face severe budget cuts that could mean delays or cancellation for the project.

Even some leading supporters of the space station have expressed concern about the country's financial ability to carry through with the commitment unless President Reagan intervenes, according to several Capitol Hill sources.

The teams led by McDonnell Douglas, of Huntington Beach, Calif., and Houston, and Boeing, of Huntsville, Ala., won the long and intense competition by defeating ones led by Rockwell International and Martin Marietta.

Two contract awards -- to General Electric's Astro-Space Division, of Valley Forge, Pa., and East Windsor, N.J., and to Rocketdyne Division of Rockwell International, of Canoga Park, Calif. -- were uncontested.

Sources familiar with the awards said that where there were competing bids, the costs "seemed to be low, while in the proposals where there was no competition, the costs seemed high."

The four teams won the right to negotiate terms with NASA for work on space station hardware that could total $6.5 billion and provide an estimated 12,000 jobs around the country, mostly in California, Alabama, Texas, Florida, Pennsylvania and New Jersey. Reston is the headquarters for space station management.

The permanently manned space station is described by its supporters as a symbol of the United States' will to compete with the Soviet Union in space. The Soviets have lofted manned stations since the early 1970s. And today a Soviet cosmonaut aboard the space station Mir will pass the 300-day mark, nearly four times longer than an American has stayed in space.

Radio Moscow has announced that the current Mir crew will land on New Year's Eve after being replaced by a crew that is expected to try to stay in orbit for one year.

Sen. Ernest F. Hollings (D-S.C.), chairman of the Senate Commerce, Science and Transportation Committee, yesterday called on the president to "lead the effort to convince the American people of the value of the space station as a symbol" of U.S. competitiveness with the Soviet Union.

"NASA took a bold step {yesterday}, and I salute them," he said, "But we are running a marathon. {We} require more support from the president. . . . The race for space didn't end with the Apollo program. It's just beginning."

NASA Administrator James C. Fletcher, announcing the awards at Goddard Space Flight Center in Greenbelt, said the competing contract proposals were approximately even in terms of costs, once uncertainties were considered, so the final selection was based almost entirely on technical factors and the companies' suitability for the mission.

"The best minds of the nation went to work on this competition and all of the proposals . . . were outstanding," he said, adding that the winning proposals were "clearly superior."

The orbiting laboratory, scheduled to be assembled in space in the mid-1990s, would include two habitable modules provided by the United States and, assuming negotiations are successful, one by Japan and one by the European Space Agency. Canada is also expected to provide equipment.

Fletcher said he does not yet know how current budget maneuvering will affect the space station or its schedule. Some Capitol Hill sources suggested the cuts for this fiscal year could take funding as low as $420 million. (The administration had requested $767 million.) More serious problems could arise in fiscal 1989, when funding was projected to climb to $1.8 billion.

Sen. William Proxmire (D-Wis.), who has sought to kill the space station, said, "The chances are fairly strong that there will have to be a period of redesign to bring the station back to Earth cost-wise."

Sen. Donald W. Riegle Jr. (D-Mich.), chairman of the Senate science, technology and space subcommittee, predicted that a permanently manned U.S. facility will be in orbit "by the end of the century," somewhat later than planned.

The amount of budget cuts will not be known until mid-December, according to congressional sources.

Rocketdyne will build the power-generation and -distribution system, including arrays of solar panels. The McDonnell Douglas contract is for a metal truss forming the backbone of the station plus nagivation, communications, airlock and propulsion equipment.

Boeing will build two modules for use as laboratory and crew quarters plus environmental and life-support systems. General Electric's contract is for a free-flying platform that could carry scientific instruments and a robotic satellite-servicing system.