Ear-splitting military training flights over this densely populated country became a major issue in West Germany in 1988 because of a series of crashes, and opponents have vowed to step up their campaign this year.

"This self-imposed threat from the skies must end. Our populated areas must above all be safe," Erwin Horn, a federal lawmaker with the opposition Social Democrats, said Tuesday.NATO pilots resumed tactical flights over West Germany on Tuesday following a three-week moratorium in memory of the victims of a Dec. 8 crash of a U.S. military jet on the northern city of Remscheid. Five West Germans and the U.S. pilot were killed.

Critics insist on more than a moratorium and say they will step up their pressure for NATO forces in West Germany to abandon low-level training flights, in which planes fly at altitudes as low as 250 feet.

"We want military low-level flights to stop permanently," said Werner Mey, head of the nationwide protest group, "Coordination of Opponents of Low-Level Flights."

"There will be a whole spectrum of (protest) actions this year," Mey said in a telephone interview from his home in Biebelnheim near Mainz.

The screeching of NATO jets on low-flying training maneuvers occurs frequently in West Germany, where air bases are scattered across the country.

A series of military air crashes in 1988 has ignited widespread opposition among the West German populace to NATO low-level training flights.