Astronauts Thomas K. (Ken) Mattingly and Henry W. Hartsfield flew to the Kennedy Space Center today to begin final preparations for the first secret mission to be flown by the space shuttle Columbia.

Mattingly and Hartsfield flew their T38 jet trainers from Houston's Johnson Space Center, setting down on the shuttle landing strip at 4:25 p.m. EDT. They were taken immediately behind closed doors for final briefings. The astronauts are to fly Columbia into orbit at 11 a.m. EDT Sunday on the fourth and last test flight of the craft, a flight that will also take 2,000 pounds of classified instruments into space for the U.S. Air Force.

The planned seven-day mission will be the first that the civilian space agency has ever classified as secret. Security is so tight that Mattingly and Hartsfield have been ordered not to televise pictures of the Air Force instruments in Columbia's cargo bay back to Earth.

"We are entering a new era, not only for the space shuttle but for our growing dependence on space for national security," Brig. Gen. Richard F. Abel said here the other day. "Our one goal is to protect the cargo and the mission."

The Air Force instruments have been identified publicly as EOE-82-1 and classified as secret, but not before technical reports and congressional testimony indicated that the instruments include a new space sextant and a new ultraviolet telescope that will help navigate unmanned spy satellites.

Another instrument in the secret Air Force array is understood to be a supercooled infrared telescope that can follow high-flying aircraft from orbit by tracking the heat of their engine exhaust. The instrument, developed at Utah State University, is called CIRRIS, for Cryogenic Infrared Radiance Instrument for Shuttle.

Mattingly and Hartsfield, both graduates of Auburn University in Alabama, are also former military test pilots, one reason they were selected to fly the shuttle on its first secret mission. Mattingly, 46, is still a Navy captain. Hartsfield, 48, is a retired Air Force colonel.

When they were asked what they thought of flying in space in secrecy, Mattingly replied: "Space is a place. It's a place where people live and work, and it's not different than the oceans and the earth we live on."

Mattingly's and Hartsfield's flight plan is the first that will not take a manned American spacecraft over southern reaches of the Soviet Union. The shuttle's orbit will go no farther than 28 degrees north or 28 degrees south of the equator.

The National Aeronautics and Space Administration says that upcoming flights of the space shuttle will take the same orbital track, in part because civilian users of the shuttle want to leave communications satellites in orbit as close as possible to the equator to give them wider coverage of the Earth.

Others familiar with the space program, however, believe the flight path for the next shuttle mission is being followed so as not to antagonize the Soviet Union, which has charged that the shuttle is an instrument of war.

The shallow inclination to the equator means that the shuttle will be out of communication with American tracking stations far more than on previous flights. To compensate, Mattingly's and Hartsfield's orbit will be about 30 miles higher than the three previous shuttle crews'.

"The higher orbital altitude means we'll lose about 15 percent of our communications coverage," said Jay Honeycutt, shuttle manager of operations integration. "If we hadn't gone to a higher altitude, we'd lose about 20 percent of our coverage."