As NATO warplanes step up the pace and number of their airstrikes on Yugoslavia, Belgrade's air defense forces are responding for the first time with ferocious volleys of antiaircraft fire and surface-to-air missiles, alliance officials said today.

NATO authorities said the latest 24-hour phase of the air campaign drew 33 surface-to-air missile attacks on allied planes, more than at any time since the airstrikes began in late March. One pilot reported that a missile exploded so close to him that his plane shook.

"A sense of desperation is setting in as they make a last determined stand to shoot down at least one of the NATO planes, because they want one last victory," said German Air Force Maj. Gen. Walter Jertz, a NATO military spokesman. In more than 27,000 NATO missions since the start of the air campaign, the Yugoslavs have downed only two planes, and no NATO pilots have been killed or captured.

During the first weeks of the air war, NATO strategists were puzzled by the absence of antiaircraft fire from Yugoslav defenses. They concluded that air defense operators were hunkered down in a "survival mode" to protect themselves from being attacked once they turned on their radar systems to track allied planes.

"That's when we realized that nobody wanted to eat a HARM missile for [Yugoslav President] Slobodan Milosevic," said Lt. Gen. Michael Short, NATO's top air war commander, in an interview last week at his headquarters in Vicenza, Italy. He was referring to the highly accurate anti-radiation missiles carried by many NATO aircraft to neutralize ground radar systems.

While recent clear weather has made it easier for NATO pilots to identify their targets, it also has helped Yugoslav antiaircraft operators track incoming planes without having to turn on radar that would betray their locations.

NATO officials said alliance aircraft flew a record number of sorties today -- 741, including 308 attack missions and 74 others designed to suppress air defense systems.

Airstrikes Wednesday night and early today hit a wide range of targets, the officials said, including 10 artillery positions in Kosovo province -- the focus of the nine-week-old conflict. At least five tanks, eight armored personnel carriers and four antiaircraft artillery emplacements also were hit.

Other targets struck included ammunition storage sites, radio and television transmission and relay sites, oil storage tanks, airfields and army and police barracks buildings, the officials said.

Power facilities around Belgrade were also hit again. Two major power distribution stations in the capital were struck, and residents said much of the city remained without electricity for most of the night.