Libya has accelerated efforts to make its second SA5 antiaircraft site operational and is expected to have at least some missiles at the site, the coastal city of Benghazi, ready to fire by mid-April, administration officials said yesterday.

The first SA5 site, at Surt, was back in operation shortly after U.S. Navy bombers attacked it for a second time March 24 with HARM missiles, which track radar beams to their source -- in this case, protruding antennas.

The HARM missiles did little damage at Surt except to the radar antennas, and administration officials said several of the SA5 missiles on the 12 launchers at the site are back in operation. The High-speed Anti-Radiation Missile, costing the Navy almost $300,000 each, is not designed to inflict widespread damage. (The Pentagon's newest weapons book shows the Navy buying 825 of the missiles for $238.3 million in fiscal 1986.)

In a standard bombing run, the HARM missiles would have been fired just before diving at the site -- the object being to render the SA5 harmless during the few minutes the bombers were over the site.

In last week's clash, Navy planes were loaded with Rockeye cluster bombs designed to cover acres of ground with shrapnel. No Rockeyes were dropped on Surt, although the U.S. plan, code-named Operation Prairie Fire, allowed for this if any Navy planes had been downed by the missiles.

The other high-tech weapon used against Libya last week was the Harpoon antiship missile, which Navy ships and aircraft fired. Its price tag for the current fiscal year is $860,000 per missile.

Donald A. Hicks, undersecretary of defense for research, said yesterday that, as far as he knew, the HARM missiles performed well at Surt. He added that it was no surprise to him or other Pentagon weapons specialists that the six SA5s fired from Surt at Navy planes missed. The missiles were at their "outer range," he said.

Although Hicks did not say so, Navy weapons experts have never considered the SA5 much of a threat to high-speed, agile planes such as the F14 and F18 fighters and A6 and A7 bombers on the three carriers deployed off Libya last week.

The SA5 is considered primarily a threat to high-altitude, slow-moving aircraft such as transports and command and control planes.

However, U.S. officials said the accelerated Libyan effort, with Soviet help, to make the Benghazi antiaircraft site operational indicates that Libyan leader Muammar Qaddafi still has faith in the SA5, at least as a symbol of determination to repel those who cross the imaginary "line of death" he has drawn across the Mediterranean Gulf of Sidra at 32 degrees 30 minutes north latitude.

Another interpretation offered yesterday is that Qaddafi has no alternative to using the SA5s at Benghazi and Surt to cover the gulf because of a shortage of pilots and high-performance fighters to repel invaders.

Sources said that during the Navy attacks Libya put six Syrian pilots in cockpits but that they refused to fly over the gulf to take on U.S. Navy planes.

Libya's Achilles' heel, defense officials said, is not hardware but skilled manpower, such as pilots, radar technicians and electronics specialists.

Libya is heavily dependent on Syria and the Soviet Union for these skills, specialists said.