KATYN FOREST, Russia (AP) _ A somber trumpet echoed through Katyn forest Sunday as Polish President Lech Walesa and weeping mourners honored thousands of officers massacred in secret by the Soviets in World War II.

``We want to promise all victims that, in the name of human solidarity, we will remember them,'' Walesa said at the solemn memorial service by a flower-covered mass grave.

Soviet dictator Josef Stalin's secret police shot 4,400 Polish officers in 1940 and dumped them into common graves in the woods of western Russia near Smolensk and present-day Belarus.

The officers were shot in the back of the head and their bodies buried in large pits.

Another 10,600 officers, the cream of Poland's intelligentsia, were shot to death in April and May of 1940 and buried elsewhere in the former Soviet republic.

The Polish president laid a metal plaque paying tribute to those killed in the forest, praising them as sons of Poland. The slab, decorated with a simple cross, will be part of a major new memorial erected by Poland.

Walesa said telling the truth about the Soviet massacre of Polish officers in this forest was a step toward reconciling Russia and Poland.

The officers were captured by the Soviet Union when it invaded eastern Poland in 1939, shortly after Hitler sent his soldiers across Poland's western border to start the war.

The Nazis, who invaded the Soviet Union in 1941, discovered the bodies in April 1943.

Moscow did not officially admit the massacre until 1990. During the postwar decades of Soviet-imposed Communist rule in Poland, the Kremlin insisted the Nazis were to blame, despite overwhelming evidence to the contrary.

Walesa denounced the Stalinist system that carried out, then covered up the massacre.

``They were supposed to die and to leave behind only the dark silence,'' he said of the fallen officers. Instead, ``the systems pass away. But the truth stays, the truth prevails.''

Russian President Boris Yeltsin, who declined to attend the memorial, sent a message to Walesa saying the truth would lead to better relations between Warsaw and Moscow. Yeltsin said he did not attend because some Polish groups might make unreasonable demands for compensation or apologies.

``It is necessary to turn this tragic page of our joint history,'' Yeltsin said.

He also noted that Stalin's henchmen had buried more than 10,000 other victims of various nationalities in the forest.

``We consider this forest a memorial for the victims of totalitarianism, (a place) where a monument to all the innocent victims should be created,'' he said.

Russian war veterans as well as relatives of the officers endured sweltering heat during the three-hour ceremony.

A Polish army band played patriotic songs and about 200 mourners softly sang hymns. Poland's Cardinal Jozef Glemp presided over the ceremony. He was assisted by Russian Orthodox priests and clergymen from both Poland and Russia.

Many people wept as the Polish trumpeter played mournfully.