ARECIBO, Puerto Rico -- The Arecibo Observatory, home of the world's largest radio-radar telescope, has moved close to completion of a major upgrade that makes it one of the most sensitive and powerful tools ever designed for astronomical studies.

The observatory, operated by Cornell University's National Astronomy and Ionosphere Center under a cooperative agreement with the National Science Foundation (NSF), on May 16 completed installation of a new system for focusing incoming radio waves that will open new doors to the universe.

On May 16, the 90-ton, 85-foot diameter Gregorian system enclosure was hoisted from the bottom of the 1,000-foot diameter reflector to its working position 450 feet above, on the azimuth arm. The lifting process took about two hours, starting in the pre-dawn mist at 6:10 a.m. The construction work, part of a $25 million upgrade of the Arecibo telescope financed by the NSF and NASA, was begun in 1993. COMSAT RSI of Sterling, Va., is prime contractor for the work.

Remember that big dish that appeared out of a lake, then was blown to bits in the climactic scenes of the James Bond movie Goldeneye? Well, the dish remains (although it doesn't rise from under water -- it's fixed in a huge sinkhole in the hills of northwest Puerto Rico), but the system suspended above the dish to focus the radiowaves collected by the 1,000-foot-diameter (305-meter) reflector has been radically changed.

Now, a new six-story, 90-ton dome houses a new reflector system, a combination of two radio mirrors and sensitive receiver systems. It is suspended 450 feet above the giant 1,000-foot reflector dish. The mirrors focus radio waves coming from distant objects in space, or radar signals that are sent out into space and bounce back from the surfaces of the planets and other bodies in the solar system. "First light" is expected by the end of August.

"We are delighted that we will soon have a new much more sensitive and versatile telescope," said Paul Goldsmith, director of the National Astronomy and Ionosphere Center and Cornell professor of astronomy. "It will open a new era of radio astronomical observations of pulsars, distant galaxies and our own galaxy. We are looking forward to a host of new discoveries."

Also, "The new radar system will have a tremendous capability to image Earth-approaching asteroids and comets," said Don Campbell, associate director of NAIC, as a 1-km asteroid is set to pass within 2 million miles of Earth on May 25.

The upgrade includes a doubling to 1 megawatt of the power of the transmitter used for radar studies of the solar system, a 50-foot-high stainless steel mesh fence (called a ground screen) to reduce the effects of interfering radio noise emitted by the ground around the perimeter of the reflector dish, reinforcement of the existing 600-ton suspended structure and installation of additional supporting cables to carry the added weight of the dome. The fence was installed in 1993.

The upgrade gives the Arecibo telescope such better sensitivity: It could be used to listen into a cellular telephone call on Venus; the radar could detect a steel golf ball at the distance of the moon. The new system increases the telescope's sensitivity by a factor of about 20 for radar studies of the solar system -- comets, planets, moons and asteroids. Studies of the radio waves from distant galaxies, pulsars, quasars and other objects can be made 10 times faster with the new focusing system, and the much greater frequency coverage (300 MHz to 10,000 MHz) will open up new studies of molecules in star-forming regions of our own galaxy.

A spherical reflector such as the Arecibo dish does not focus radio waves to a point as does a parabolic satellite antenna, but the symmetry properties of a sphere mean that it is possible to "steer" the telescope to look in different directions by moving the focusing system rather than the entire 1,000-foot reflector. The original focusing system consisted of long, linear wave guide elements (the villain in Goldeneye fell from the bottom of one of these) which have many disadvantages; a different one is needed for each frequency, and they are very difficult to build, virtually impossible at frequencies above about 3,000 MHz.

The new system does it with mirrors, one about 80 feet in diameter, the other about 28 feet, called a Gregorian system. The mirrors are enclosed in the dome along with the new radar transmitter and microwave receivers. The whole structure is attached to trolleys moving on the 300-foot-long curved feed arm suspended above the dish.

Thus, the new Arecibo Observatory holds promise for decades of new discoveries, as it opens up new areas of research. Here is an example of some of the science that can be investigated:

• Birth of stars. New stars form out of cold clouds of dust and gas, which emit no visible radiation. But the molecular material in these clouds emit radiation at radio wavelengths. "The high sensitivity and broad frequency coverage of the upgraded Arecibo Observatory will allow detection and study of a range of very heavy molecules in these coldest regions of the galaxy," Goldsmith said. Thus, scientists will have a new tool to study the chemical and physical conditions in the regions where new stars and planets around them form.
• Extra-galactic studies. Astronomers studying the large-scale structure of the universe will have a much improved ability to measure velocities and masses of galaxies, which in turn can yield clues to the distribution of "missing matter" in the universe.
• Comets, like Comet Hale-Bopp that will be visible this fall and Comet Hyakutake which was visible from Earth in March, and near-Earth asteroids can be studied in far greater detail, with the upgraded radar system at Arecibo.
• Pulsars can be examined more closely, and more of them become accessible, with the increased sensitivity. The first planets outside our solar system were discovered around a pulsar using the Arecibo Observatory.