The first American woman to rocket into space stood as ready as her name suggests to ride the space shuttle Challenger into orbit on Saturday with four male astronauts and make space history.

If all goes well, Sally K. Ride, 33, will join two Soviet cosmonauts as the only women to enter space in the 22 years that men almost routinely have been making flights from Earth. Liftoff time for Ride and astronauts Robert L. Crippen, Frederick H. Hauck, John M. Fabian and Norman E. Thagard is set for 7:33 a.m. EDT.

Ride, who was recruited with five other women in 1978, has waited five years for her first flight. Though she must be considered a pioneer, she follows 57 male astronauts, and her mission is the 37th "manned" American space flight.

In a message to a VIP reception here tonight, President Reagan said: "Challenger will open a new era of greater opportunity. This mission will mark not only the first ascent of an American woman into space but also the shuttle's first all-foreign primary payload and a host of new experiments. In every sense, space is becoming the province of all humankind . . . ."

The president sent his prayers to the crew and added: "And may the Force be with them."

"I think this milestone could have happened a lot sooner, but the fact is that it's finally taking place and it's taking place tomorrow," said Air Force Lt. Gen. James A. Abrahamson, associate administrator of NASA, at a pre-launch news conference. "But this is only the first milestone. The second milestone will come when we have ladies going into space and not even being noticed when they go."

There is no chance of that happening here on Saturday. By late today, more than 1,200 members of the press and as many as a half-million spectators had crowded into Brevard County, where the Kennedy Space Center is located, to watch the seventh flight of the space shuttle, the second of Challenger and the first by an American woman.

"Sallymania" they're calling it here along the beaches of Florida's space coast. It is a condition so virulent that it may last until next Friday when Challenger returns from Earth orbit to make the shuttle's first landing at the Kennedy Space Center, where previous flights only began. Five of the first six flights landed at Edwards Air Force Base in California and a sixth at the White Sands Missile Range in New Mexico.

Brevard County police today said they expect that crowds may be even larger at landing than at liftoff, in part because President Reagan is coming to Florida to witness the landing and in part because Floridians have seen dozens of liftoffs but never a landing.

"You've got to remember that most of the visitors we get for a space shot are people who live in Florida," said Bill Lyerly, director of the Brevard County Chamber of Commerce. "Since this is the first landing we've ever had, we don't know what to expect."

Except for police and the chamber of commerce, nobody was thinking today about crowds. All eyes and ears were on Ride, the doctor of astrophysics from Stanford University.

Two women have been in space before. The first was 20 years ago this week when 26-year-old amateur sky diver Valentina Tereshkova was hurried into space for three days not long before the Soviet Union played host in Moscow to the World Congress of Women. The way American astronauts who have talked to Soviet cosmonauts tell it, Tereshkova was sick and near hysterics most of her time in space, at least in part because she received so little training for her hurried flight.

The second time was last August when 34-year-old test pilot and parachutist Svetlana Savitskaya flew in Salyut 7 with three other cosmonauts. Nobody knows what her tasks were in space but when she left her Soyuz spacecraft and came aboard the space station, one of the two cosmonauts manning the Salyut joked that her apron was ready for her.

Cosmonauts privately have told astronauts that one reason the Soviet Union waited so long to send a second woman into space was Tereshkova's bad experience in orbit the first time. Astronauts have said there is no chance of that happening Saturday when Ride becomes the first American woman in space.

Ride has trained as hard as any of her male colleagues for the last five years. She has become expert in manipulating the 50-foot-long robot arm that she and Fabian will use on their third, fourth and fifth days in orbit to deploy and retrieve a 3,200-pound instrument package.

"Fabian and Ride are very, very good at manipulating the arm," Gen. Abrahamson said at today's news conference. "They have had over 300 simulations with the arm in grappling that instrument package and bringing it back to the payload cargo bay."

Ride also will join Fabian in deploying two communications satellites on their first and second days in space. One satellite will be deployed for Canada late on the first day, the other will be moved out of the cargo bay on the second day for Indonesia.

"All I know is, this is a very relaxed crew," Abrahamson said. "They were all out running this morning. They're in real good shape and they're ready to go."

The liftoff of the space shuttle Challenger, which is scheduled for 7:30 a.m. Washington time, will be broadcast live on the three major television networks. NBC will start its coverage at 7 a.m.; ABC and CBS will begin coverage at 7:30.