BRUSSELS, Belgium (AP) _ West Germany, the Netherlands and Belgium sharply criticized the Soviet Union Wednesday for not informing them sooner about the pilotless MiG-23 fighter jet that careened out of control over their territory.

A NATO commander joined the Netherlands and Belgium in calling for better East-West cooperation to avoid such incidents.

The Soviet fighter plane took off Tuesday from Poland on a training flight, but its pilot ejected after a mechanical problem developed, according to Tass, the official Soviet news agency. The jet, apparently still on automatic pilot, entered West Germany, crossed the Netherlands and crashed Tuesday near a heavily populated area in Belgium, killing one man in his home.

NATO officials said two U.S. Air Force F-15 aircraft shadowed the MiG as it flew for 560 miles over the three NATO countries but did not try to shoot it down for fear of spreading flaming debris over cities and towns.

''You can't just go up and shoot the plane down,'' said Lt. Col. Bernard Beck, a spokesman for Allied Forces Central Europe in Ramstein, West Germany.

''West Germany is densely populated and you don't know where the plane will fall if you shoot it down at 30,000 feet. The risk factor is too great.''

About 75 minutes elapsed between the time NATO first detected the plane and the time it crashed.

West Germany, the Netherlands and Belgium protested they had to wait more than 10 hours before Tass provided Moscow's first reaction to the incident.

Soviet Defense Minister Dmitri Yazov said Wednesday an investigation in Poland and at the crash site would try to determine why Warsaw Pact forces failed to detect and shoot down the plane. ''It is difficult to say why it was not shot down, why it was not detected,'' Yazov told Tass.

A military report to the Soviet Parliament said Soviet commanders learned within 90 seconds the pilot had bailed out but that they were still searching for the plane when its crash was reported by Western news agencies.

Soviet President Mikhail S. Gorbachev, who is on an official visit to France, said: ''I regret this incident. The Belgians know. The Belgians know the cause. This type of accident can happen.''

In Brussels, Foreign Minister Mark Eyskens summoned Felix Bogdanov, the Soviet ambassador, to discuss the crash. Afterward, Eyskens said the Soviets were ''extremely slow'' about notifying NATO countries.

To avoid such incidents, Belgium called for an improved flow of information between the North Atlantic Treaty Organization and the Soviet-led Warsaw Pact.

''My conclusion, corroborated by the Soviet ambassador, is that information systems have to be improved between the two blocs,'' Eyskens said. Belgium will ask the NATO alliance to discuss such improvements, he said.

The Netherlands said it wanted ''measures that will prevent any such incident in the future.''

The West German government was angry that ''nothing was done to inform governments involved about the incident,'' Foreign Ministry spokesman Hanns Schumacher said in Bonn.

The Belgian army started clearing the crash site 50 miles west of Brussels and prepared to take the wreckage to a Belgian air force crash investigations unit.

''There it will be sealed to make sure no pieces get lost'' before it is turned over to the Soviets, said Lt. Jan Keuleers of the Belgian air force. Eyskens said the Soviet Union offered to pay for damages caused by the crash.

U.S. Lt. Col. Michael R. Gannon, a spokesman at NATO's Supreme Headquarters Allied Powers Europe based in southern Belgium, said there were no plans for NATO experts to examine the plane.

Eyskens said NATO should set up new early warning measures. ''There is a hot line between the United States and the Soviet Union, but this incident shows that there is a weakness in the flow of information,'' he said.

Gen. Hans-Henning von Sandrart, the West German commander of NATO forces in Central Europe, said in West Germany that a hotline should be set up between NATO and the Warsaw Pact that would make it easier for the alliances to exchange information in similar cases in the future.

In an interview with Saarland radio, he said neither Poland nor East Germany informed the West about the errant plane, probably because the Warsaw Pact, unlike NATO, does not have an integrated air defense.

Two years ago, West German teen-ager Mathias Rust flew a light aircraft undetected across hundreds of miles of Soviet airspace before landing in Moscow's Red Square. His stunt prompted a shakeup in the Soviet military.