THE BALKANS : U.S. Envoy Draws on Popularity in Urging Croatia to Let U.N. Stay : Ambassador Peter Galbraith, with a high approval rating and celebrity status, faces diplomatic challenge over future of peacekeeping efforts.

When Peter Galbraith, the U.S. ambassador to Croatia, took a date to the movies here several months ago, he was greeted by a spontaneous round of applause from the packed cinema.

“Look, it was deeply satisfying,” the 44-year-old envoy said later, laughing. “I just wish it wouldn’t happen on a date .”

As the applause suggests, Galbraith has, in his 20 months on the job, become a celebrity. But he is also a recognized diplomatic force in Croatia, the northwestern neighbor of Bosnia-Herzegovina and headquarters of the 44,000-member U.N. Protection Force deployed in the Balkans.

The first American ambassador to this young country of 4.7 million people has traveled extensively and won praise for speaking bluntly. In a recent opinion poll, Galbraith won an 82% approval rating, second only to President Franjo Tudjman.

Now, though, Galbraith faces his most difficult task. He is desperately trying to use that reservoir of good will to persuade Croatians to rescind their decision to expel the 12,000 U.N. troops monitoring a cease-fire in their country.

Tudjman says the U.N. soldiers have created a stalemate that has prevented the government from taking back the one-third of the country still held by 300,000 rebel Serbs demanding independence.

But the force has also maintained a 10-month-old cease-fire. The U.S. government and most other Western nations believe that removing the U.N. troops could quickly lead to a renewal of heavy fighting in Croatia, as well as increased fighting in Bosnia-Herzegovina.

“We feel it will create a very dangerous situation,” Galbraith said in an interview. “In the end, there’s only so much we can do. Ultimately, the responsibility for peace in the Balkans rests with the parties themselves.”

The frustrations of diplomacy in this region were highlighted earlier this month, when Galbraith and three other diplomats unveiled an autonomy plan for Croatian Serbs living in the rebel-held area.

The Croatian government said parts of the plan could be the basis for a negotiated solution to end the crisis. But the rebels refused to even look at the plan, which would have granted them everything from their own flag to their own currency.

Galbraith did not hide his irritation, telling reporters that it was hard to believe that the rebels preferred to continue “living in some of the most primitive conditions in Europe, which are becoming more primitive by the day.”

Galbraith is a political appointee but no stranger to foreign affairs. For 14 years before his appointment, he was senior adviser to the Senate Foreign Relations Committee.

Pakistani Prime Minister Benazir Bhutto in her autobiography credited Galbraith with securing her release from prison in 1984.

Later, much of his energy was focused on the Kurds and their battles with Iraq. In 1991, he traveled with Kurdish rebels, narrowly escaping to Syria as the rebellion collapsed.

In recent weeks, Galbraith has been a regular on television interview programs, and his photograph has been on the front pages of local newspapers.

His campaign to promote his autonomy plan and urge Croatians to rethink the expulsion of the United Nations even prompted a local journalist to ask Tudjman if Galbraith was not “meddling in Croatia’s domestic affairs.”

Tudjman, 72, defended Galbraith, saying, “He wants to find a peaceful solution and is afraid of a wider war.”

A lawyer by training, the ambassador is the son of renowned liberal economist John Kenneth Galbraith. And, to the delight of the Zagreb tabloid press, he is divorced. In a two-page spread last summer on Galbraith’s personal life and the women he has dated, the Zagreb women’s magazine Gloria called him “the most attractive diplomat in town.”