WASHINGTON (AP) _ The Air Force is refusing to discuss a report on the orbit of its newest spy satellite that raises questions about the satellite's mission and fate.

The report consists of a description of the orbit of the secret satellite carried into space last January by the space shuttle Discovery. The Defense Department is required to describe the initial orbits of all its satellites to the United Nations under international treaty, and that information was released Friday at the Pentagon.

The description of the ''orbital parameters,'' however, immediately aroused interest. The orbital path, unless it has been changed since the required U.N. report was compiled, would suggest either that the Pentagon has experienced some problems with the satellite or that published reports about its mission and destination were erroneous.

Most American spy satellites are launched into fairly low, circular orbits that pass across the earth's polar regions, or into ''geosynchronous'' orbits 22,300 miles over the equator where the satellite matches the earth's rotation and actually hangs over one region of the earth.

The satellite carried into space on the shuttle Jan. 24, however, was placed initially in an elliptical orbit that carries it to a high altitude of 21,495 miles and a low point of just 211 miles. Moreover, the Air Force said Friday the satellite was placed in an orbit with a low angle above the Equator - 28.4 degrees - meaning it was not meant to circle the earth's polar regions.

''It is unusual,'' said Marcia Smith, an expert on Soviet space developments at the Library of Congress who also follows American programs. ''I know of no operational orbit like this.''

Before the January launch, the satellite became the subject of numerous press reports following a Washington Post account of what was supposed to be a secret mission. Other news organizations, including The Associated Press, reported the satellite was designed to intercept radio, telephone and satellite transmissions as well as radio telemetry data from Soviet missile tests. Those reports quoted sources as saying the satellite was destined for a geosynchronous orbit 22,300 miles over the Soviet Union.

Efforts to determine the significance of the elliptical orbit were unsuccessful Friday. The Air Force refused to discuss any of three possible explanations, and other Pentagon officials declined to comment.

The first explanation involves the possibility the satellite has since been shifted to a new orbit. The Air Force, citing the need for mission security, refused to discuss whether the satellite was still in the orbit reported to the U.N.

A second possibility would be that rockets on board the satellite failed to function properly. Any satellite bound for a geosynchronous slot moves first into an ellipitical orbit. When the satellite is at its high point, rocket motors are fired to stabilize the satellite at that altitude and circularize its path.

The Air Force also refused Friday to say whether the satellite was working properly.

The third possibility is that despite the initial elliptical path, the satellite was never meant for geosynchronous orbit. That would contradict the description of the satellite given to reporters before the launch by various sources.