Space shuttle Discovery's astronauts today made a clean sweep on their third day in orbit, successfully deploying a third communications satellite on the maiden voyage of the nation's newest spaceliner.

"Congratulations," astronaut Dick Richards called from the Mission Control Center in Houston. "You guys are three for three."

The crew also successfully tested an experimental solar-power device, extending it to most of its 10-story length.

The satellite expelled from the shuttle cargo bay today was a Telstar owned by American Telephone & Telegraph Co. and is the third of a new series that can handle four times more telephone calls than most other communication satellites.

AT&T paid NASA $10 million to carry the satellite into orbit, bringing to $34 million the revenue this flight has generated from the three satellite launches. Satellite Business Systems paid $8.8 million for its satellite's deployment and Hughes Aircraft Corp. paid $15.2 million to have its Leasat (leased satellite) launched by Discovery.

NASA still is losing money on the shuttle flight program even though the $34 million was the highest revenue from any of its 12 flights.

Discovery's flight cost NASA about $125 million, half what each of the first four flights cost.

After the crew, including Henry W. Hartsfield Jr., Michael L. Coats, Richard M. Mullane, Judith A. Resnik, Charles D. Walker and Steven A. Hawley, put the third satellite into orbit today, President Reagan called them from the Oval Office.

"How's it going?" Reagan asked. "Any surprises?"

"I guess for the five rookies here, it's a big surprise for them," flight commander Hartsfield replied. "This is such a tremendous ride, you ought to try it sometime yourself."

"You mind if I think that over?" Reagan responded.

Reagan then turned his attention to Resnik, the second American woman to fly in space and who has a doctorate in electrical engineering from the University of Maryland. "Is it all you hoped it would be?" the president asked.

"It certainly is," Resnik replied, "and I couldn't have picked a better crew to fly with."

Late in the day, Resnik deployed about three-quarters of the 10-story-tall experimental solar panel from the shuttle cargo bay to test its flexibility, dynamics and strength as the spaceliner circled the Earth at 17,500 miles an hour.

Looking out of a cabin window, Hartsfield said the huge solar panel "is not budging one iota. It's as solid as a rock."

The solar panel will be extended to its full 10 stories on Sunday, Monday and Tuesday. It is designed to supply enough auxiliary power to double the 10-day endurance of the shuttle in orbit.

About the only trouble the crew had today was with the miniature pharmaceutical factory that is producing a hormone for Johnson & Johnson and McDonnell Douglas Corp. The two companies have refused to identify the hormone on grounds that it is proprietary information that they want to keep from competitors.

A refrigerator-sized machine purifying the hormone broke down at least twice Friday night, then shut itself down early today when a computer-controlled pressure pump ran too fast.

Payload specialist Walker, an employe of McDonnell Douglas, turned the machine on again by running the pump manually.