On a packed square where Bulgarians celebrated the end of their Stalinist government a decade ago, President Clinton praised this Eastern European nation today for turning its eyes and ambitions to the West. He promised more help from the United States if Bulgaria continues its movement toward democracy and a reliable economic system.

As several thousand people cheered and waved flags in the broad square before the Nevski Cathedral, with a full moon just starting to rise, Clinton hailed Bulgaria for throwing off communism and holding fair elections, even as he acknowledged the path has been bumpy.

"Communist rulers . . . fed you lies, yet you sought the truth," he said. "When the Cold War ended, it took much longer for the ground here to thaw."

Bulgaria, like Romania, has found it difficult to evolve from life as a Soviet satellite, suffering crippling inflation and unstable governments until 1997, when Petar Stoyanov was elected president and the economy began to find its feet. Clinton spent a busy day here not only to encourage that transition but also to draw a distinction between Bulgaria and its neighbor, Yugoslavia.

While many Bulgarians disapproved of the U.S.-led bombing of Yugoslavia during the Kosovo conflict, Stoyanov's government did not openly condemn the NATO campaign. Clinton, the first U.S. president to visit this country, returned the favor today. Standing next to Stoyanov, he told the crowd, "you stood with NATO" when the Yugoslav president, Slobodan Milosevic, threatened the promise of an "undivided, democratic" Europe.

"I know it was very hard for you to do," Clinton said. "I am told that during the recent war, you could actually hear some of the bombs falling in Serbia from this square. Tonight, I hope the people of Serbia can hear our voices when we say, 'If you choose as Bulgaria has chosen, you will regain the rightful place in Europe Mr. Milosevic has stolen from you, and America will support you too.' "

Clinton will be able to take that message right to Yugoslavia. He is scheduled to travel to Pristina, capital of Kosovo, and a nearby U.S. military camp to speak to local residents and U.S. troops trying to keep peace in the battered Serbian province.

The Kosovo visit will be the climax of Clinton's 10-day trip to southeastern Europe, which included stops in Turkey, Greece and Italy.

In his speech at the square here, and at an earlier luncheon with several college students, the president called on Balkan residents to drop old ethnic hatreds and integrate themselves into European culture and economics. Again citing Milosevic's repression of ethnic Albanians in Kosovo and Muslims in Bosnia, Clinton told the thousands of people in the square: "I want to thank you for setting a very different example here in Bulgaria. . . . But you also made that choice 50 years ago, when you helped Bulgaria's Jewish community to survive World War II and the Holocaust."

Bulgaria sided with Germany in that war--as well as in World War I--but its government protected many Jews from Nazi death camps.

"On behalf of American Jews and Jewish people everywhere, I thank you for that," Clinton said.

Stoyanov, who spoke before Clinton at the square, said, "Today, 10 years along, we Eastern Europeans realize that the change has proved more difficult, more painful and slower than we had imagined. . . . After the war in Kosovo, we realized that the democratic future of southeastern Europe depends on investment, joint infrastructure, joint projects."

Clinton, saying he supports Bulgaria's hopes of eventually joining NATO and the European Union, promised some help. "Let me say . . . to those all over the world who will see this tonight on television, this is a wonderful country. Come here and help Bulgaria build the future," he said.

Clinton announced several modest programs meant to boost Bulgaria's economy. For example, the Overseas Private Investment Corp. issued a "call for proposals" to create a Southeast Europe Investment Fund, he said. It will have $150 million to invest directly in regional businesses and provide capital and management expertise.

Clinton met separately with Stoyanov and Prime Minister Ivan Kostov, held the student lunch discussion, went shopping at the White Stork gift shop with his daughter Chelsea and toured Roman ruins dating to 28 B.C., all before delivering the major speech at nightfall. In the evening he attended a state dinner hosted by Stoyanov, toured the Nevski Cathedral and stayed out late at a Sofia jazz club.

Clinton touched one Bulgarian--literally--when a woman tripped as she entered an art gallery and fell toward the president. He caught her and said, "Are you all right?" She looked at the famous visitor and said she was.

CAPTION: President Clinton greets Bulgarians who gathered in the square of Sofia's Nevski Cathedral. Clinton praised Bulgaria for its commitment to democracy. "Communist rulers . . . fed you lies, yet you sought the truth," he said.