Despite three confirmed visual sightings of the third stage of the Russian satellite-launching rocket, Dr. Fred L. Whipple, director of the Smithsonian Astrophysical Observatory in Cambridge, said last night that he would be unable to determine an orbit for the Communist moon. Whipple attributed the failure to compute the path to "highly unfavorable conditions" surrounding one of the sightings.

Whipple inferred from the brightness reported for the object that it was not the satellite, but its launching rocket, which Radio Moscow has said is trailing the satellite by some 600 miles.

Whipple said that the satellite and its rocket would be in the same orbit, but that one Alaska sighting was hampered by cloudy skies and was not sufficiently accurate for the computation program of M.I.T.'s giant IBM 704 computer.

Whipple said that reports that the object seen in Australia and Alaska varied in light intensity only confirm the theory that the observers saw the third stage of the launching rocket and not the satellite.

The University astronomer noted that the Russians probably know as little about the eccentricity of the orbit as anyone else. He predicted, however, that IGY scientists would be able to establish this fact within the next day.

Since the satellite's period of rotation has not changed, Whipple said that it will stay up for at least another three weeks--long enough for U.S. observers to see it. It will pass over the Boston area at 8:03 a.m. tomorrow.

Two meteor-tracking Super-Schmidt telescopic cameras in Canada have been alerted to watch for the satellite, but Whipple indicated that he did not feel that adequate photographs of the object could be taken until a special telescope in South Pasadena, Calif., was able to observe it. Such observation will not be possible for at least ten days.