To President Reagan, the space plane is an "Orient Express" that could whisk passengers from Washington to Tokyo in two hours.

To Air Force official Stanley A. Tremaine, interviewed in 1984, the space plane would be "a killer Air Force weapon system that can go out and get the enemy."

And for the president's "Star Wars" missile defense shield, a space plane could be the vehicle to launch thousands of tons of weaponry into orbit.

Whatever the outcome of research into super-fast planes that can fly into space like rockets but take off and land like ordinary jets, Reagan's enthusiastic endorsement in his State of the Union message Tuesday ensured that the National Aerospace Plane -- as it has now been christened -- will be a top administration priority.

"And we're going forward with research on a new Orient Express that could, by the end of the next decade, take off from Dulles Airport, accelerate up to 25 times the speed of sound, attaining low earth orbit or flying to Tokyo within two hours," the president said Tuesday night.

The Defense Department and NASA will ask Congress for more than $200 million for a research program in fiscal 1987, a steep increase from this year, when the agencies are spending less than $50 million on the technology, according to official estimates. In fiscal 1988, the total would rise to more than $300 million, with about 80 percent coming from the Defense Department.

If results appear promising after several years, officials have said, a prototype vehicle could be built for between $2 billion and $3 billion.

Some observers of space programs said they doubt Congress will be eager to fund a major new initiative this year, with budget deficits climbing and Reagan's 1985 call for a major effort to develop a space station still on the table.

But several major aerospace companies, including Boeing Co., Lockheed Corp. and McDonnell Douglas Corp., have been pursuing the relevant technologies for several years while attempting to persuade the Pentagon that a space plane would be militarily useful. And several government agencies -- including the Air Force, the Navy, the Strategic Defense Initiative Organization, the Defense Advanced Research Projects Agency and the National Aeronautics and Space Administration -- each have enough of an interest in the project to contribute some of the $200 million.

In November, the Air Force solicited industry in a classified proposal to build a model engine, airframe and facility to test the strong, lightweight materials crucial to a space plane, an Air Force spokesman said yesterday.

The military began flirting with the idea of a space plane 30 years ago, when Boeing developed a space glider called Dyna Soar. Defense Secretary Robert S. McNamara eventually killed that program, but the Air Force has been attracted to the idea ever since.

In an interview with Air Force Magazine in 1984, Tremaine, deputy for development planning in the Air Force Systems Command, explained why.

"Wouldn't it be great," he said, "if the Soviet Union suddenly found itself faced with the U.S. Air Force having a machine that could operate on its own, totally free from counteraction, capable of rapidly delivering weapons anywhere on the globe?"

More recently, Gen. Lawrence A. Skantze, Systems Command chief, said a space plane could have the "speed of response" of an intercontinental nuclear missile with "the flexibility and recallability of a bomber, packaged together in a plane that can scramble, get into orbit and change orbit so the Soviets can't get a reading accurate enough to shoot at it," according to Military Space newsletter.

John Pike, an expert on space programs at the Federation of American Scientists, said the space plane, or "transatmospheric vehicle," has long appealed to the Air Force as a way to maintain a role for fighter and bomber pilots in the space age. But it was the needs of "Star Wars," or the Strategic Defense Initiative, that got the aerospace plane off the ground, Pike said.

A colonel attached to the SDI office said Tuesday that finding a cheaper means than the shuttle to launch weapons, sensors and space stations into orbit has become a key priority. Relying on the shuttle would be far too expensive, he said.

An administration official said Reagan also was attracted by the civil and commercial potential of a space plane. George A. Keyworth II, Reagan's recently retired science adviser and a space plane booster, said last year that it could make rapid trans-Pacific travel "routine and simple," at rates comparable to what airlines now charge.

The official said that Keyworth kept Reagan informed on the program last year, and that Reagan mentioned it Tuesday because the "vigor of research" supported his "emphasis on youth" and the potential for the future. CAPTION: Picture, The Pentagon and NASA are to seek $200 million for research on National Aerospace Plane that might look like this. Ap