BRUSSELS, Belgium - An icon of the Cold War, the MiG-21 came to symbolize the military might of the Soviet Union as it squared off against the West over Vietnam, Africa and the Middle East.

Now, exactly 50 years after it entered service, the jet fighter is approaching the twilight of its career in front-line service - with NATO, the former Soviet Union's main rival.

The rugged and agile jet earned a reputation as a versatile and effective short-range interceptor with low operating costs and excellent performance. Like the AK-47 Kalashnikov assault rifle - another robust and reliable weapon that epitomized Soviet power - the MiG-21 holds a place in military history.

"It was one of the best fighters ever, very reliable, and a real challenge to all pilots who fought against it," said David Ivry, a former chief of the Israeli air force who battled MiG-21s as a squadron leader in the 1967 Six-Day War and as a commander in the 1973 and 1982 wars.

MiGs derived their name from the initials of their designers, Artem Mikoyan and Mikhail Gurevich. Codenamed Fishbed by NATO, the MiG-21 gained fame during the Vietnam War, when the North Vietnamese air force used it to intercept American bombers.

Although heavily outnumbered, the small Fishbeds could evade radar and ambush U.S. formations with hit-and-run attacks in which many U.S. jets, including top-of-the line F-4 Phantoms, were downed or forced to abort their missions.

"The MiG-21 was lighter and more agile than the Phantom, which gave it a better chance to survive in a dogfight," wrote Russian aviation historian Vladimir Babich, who analyzed the MiG's performance in Vietnam.

The U.S. Air Force first gained vital insight into the MiG-21's capabilities after a defecting Iraqi pilot flew one to Israel in 1966. The Israelis also exploited their findings during the Six-Day War, when their surprise air strikes destroyed the Arab air forces on the ground.

Although the plane's performance was enhanced over the years, designers never overcome the limited fuel capacity, stemming from the design's small size. Another weakness was thick windshield framing that reduced the pilot's forward visibility, a serious problem during combat.

Still, more than 10,000 were built, making the MiG-21 the most widely produced jet fighter ever built.

The delta-winged Mach 2 interceptor - Mach 2 is double the speed of sound - was widely exported and became the backbone of about 50 air forces in Europe, Africa and Asia. It was used in a dozen armed conflicts in the last 30 years, more than any other fighter in history.

In the 1970s, the United States introduced two jets that outperformed the MiG-21 - the F-15 Eagles and F-16 Fighting Falcons. The Soviets countered with MiG-29s and Sukhoi-27s. By the 1980s, the aging Fishbeds were relegated to second-line duties, such as reconnaissance.

Russia has long since retired the MiG-21, but it remains operational with numerous air forces.

After the collapse of the Soviet Union and the Warsaw Pact, the USSR's former East European allies joined NATO, bringing more than 200 of their aging MiG-21s into the Western alliance.

Most have since been replaced, but the old warhorse soldiers on in NATO members Romania and Bulgaria, and in Croatia, scheduled to join the alliance in 2009.