The United States employed computer-age warfare to combat old-fashioned piracy in the force-down of the Egyptian 737 passenger plane carrying the four terrorists who hijacked the Italian cruise ship Achille Lauro, defense officials said yesterday.

The Air Force, Navy and National Security Agency were deeply involved in the hunt for the plane, sources said, as an antiterrorist team of Army commandos and Navy Seals stood by on the Marine assault ship Iwo Jima in the Mediterranean.

The NSA eavesdropping net included an Air Force C135 transport tailored for electronic warfare and code-named Burning Wind, officials said. It circled in the sky off Egypt to eavesdrop on air and ground communications, sources said, as part of a broad intelligence-gathering effort to learn when the 737 would leave a military airport outside of Cairo and where it would go.

The Navy, too, deployed electronic eavesdropping planes in the region, sources said, including the A3 Skywarrior, known as the Whale because of its size, to try to record every message between Egypt and the airborne 737. Whale aircraft cover a large area of the Mediterranean by hopscotching between carriers like the USS Saratoga, which was in the area, and land bases in Spain and Sicily.

Once these and other electronic platforms learned the planned takeoff time and probable destination of the 737, sources said, Adm. William J. Crowe Jr., chairman of the Joint Chiefs of Staff, recommended to President Reagan that an intercept be attempted.

According to the Defense Department, Reagan indicated at 1:30 p.m. Washington time Friday that he liked the idea of an intercept and force-down. Anticipating final presidential approval of the plan, Crowe recommended that the Saratoga put its planes in the air. They were launched at about 2:15 p.m. Washington time.

At this time, the Saratoga broke out of its North Atlantic Treaty Organization formation in the Ionian Sea and reversed course to be near the intercept point. The United States had learned that the 737 would take off at 4:15 p.m., which gave the carrier and its planes almost two hours to get ready for the intercept.

The Saratoga, officials said, had been on alert -- with bombers and fighters armed and ready for takeoff -- since shortly after the Achille Lauro was hijacked on Monday. An intercept force of two E2C Hawkeye command-and-control planes, seven F14A Tomcat swing-wing fighters and four KA6D tanker planes for aerial refueling were launched into the night, according to the Pentagon.

Through electronic and human intelligence, the Saratoga's air controllers, sitting in the carrier's semi-dark command center, knew not only in what general direction to send the planes to cross the 737's path but even the number painted on the jet airliner's side.

The battle group commander inside the Saratoga ordered the planes to wait in ambush as the Saratoga reversed course.

The F14 fighters, gulping fuel as they waited for the 737, refueled from the KA6Ds several times, always a tricky maneuver at night since it involves spearing a bouncing fuel nozzle that trails behind the tanker. The E2Cs, propeller planes that burn far less fuel than fighters, were able to stay up without refueling.

One of the two E2Cs acted as the airborne command post, telling the fighter pilots what direction and altitude were needed to intercept the transport.

The E2C Hawkeye is packed with electronic gadgetry, including a radar that can see in all directions, including down, for more than 200 miles. The plane also has a computer that tells three operators in the back the course to fly to intercept each green dot displayed on the big radar scopes.

Operators only have to touch the dot on their radar scope with a special pencil to learn what the Hawkeye's computerized brain has stored about objects invisible to human eyes.

The E2C commander, defense sources said, directed the F14s to one dot after another before finding the quarry, the 737. The F14s intercepted and inspected at least three planes, including a military transport, before finding the 737 and forcing it to land at Sigonella in Sicily, according to the Pentagon.