In a daring and unusual move, the Jet Propulsion Laboratory here has indirectly approached President-elect Ronald Reagan with a plan to send a spacecraft to intercept Halley's Comet in 1985 -- a proposal that the lame-duck Carter administration and the U.S. space agency have previously considered and rejected.

The approach was made last week by California Institute of Technology trustee Earle M. Jorgenson, president of the Jorgenson Steel Co., and an old friend of Reagan's. Cal Tech manages the lab for the National Aeronautics and Space Administration.

To minimize costs, the lab has suggested building a spacecraft largely of spare parts from the Voyager and Viking programs, as well as components from the still-in-development Galileo project.

Because of its extensive use of proven hardware, the Halley's intercep mission is projected to cost about $250 million. That figure does not include the cost of a launch vehicle or the operation of tracking stations during the eight-month life of the probe.

The lab is understood to have decided to make an approach to Reagan now because the incoming administration soon will be drawing up its budget revisions for fiscal 1982. Lab managers believe there is no time to spare if the spacecraft is to be built, tested and readied for a 1985 launch date.