BANJA LUKA, Bosnia-Herzegovina (CNN) -- The hard-line nationalist elected president of the Bosnian Serb republic vowed Saturday to respect the Dayton peace accords.

But some Western observers expressed skepticism about Nikola Poplasen's commitment to a unified, democratic Bosnia.

Poplasen, of the Serb Radical Party, ousted moderate Western-backed incumbent Biljana Plavsic in the September 12-13 balloting, the results of which were announced Friday. During the campaign, he had said he would use all constitutional means to unite the Bosnia Serb republic with neighboring Serbia, the dominant republic in the Yugoslav federation.

But Saturday, Poplasen backed away from that provocative position and said he would do nothing to undermine the Dayton accords, which ended Bosnia's civil war and set up a power-sharing system through which Serbs, Croats and Muslims jointly govern the country.

"The time ahead of us will prove that these suspicions regarding our willingness to implement the Dayton peace agreement and to cooperate with the international community are unfounded," Poplasen said to reporters in the Bosnia Serb capital, Banja Luka.

Moderates make inroads against nationalists

Bosnians went to the polls to pick the three members of the collective national presidency -- one Serb, one Croat and one Muslim -- as well as members of the national parliament. In addition, residents of the Serb republic and the Muslim-Croat federation -- the two entities into which Bosnia is divided -- picked regional officials.

In general, moderate parties made gains against nationalist forces, a development which Western observers hope will strengthen the peace process. The incumbent hard-liner who held the Serb seat on the collective national presidency, Momcilo Krajisnik, was defeated by a more moderate candidate, Zivko Radisic.

But when it came to the presidency of the Bosnia Serb republic, the nationalists triumphed with Poplasen.

During the civil war, he was a paramilitary commander allied with Radovan Karadzic, the wartime leader of the Bosnia Serbs who is now wanted as a war criminal. And Poplasen's Radical Party is an offshoot of an ultranationalist party in Serbia, headed by Vojislav Seselj, Serbia's deputy premier.

However, Poplasen, along with his coalition partner, Dragan Kalinic, pledged Saturday to preserve "all the good that the international community and the previously moderate Serb government accomplished," as well as to strive for a democratic society based on a market economy.

Western officials were making it clear that they expected Poplasen to continue with the Dayton process if he expects Western aid to flow for reconstruction of war-torn Bosnia.

"Financial support for reconstruction will only be available for those who work together with the international community to implement the Dayton agreement," German Foreign Minster Klaus Kinkel said Saturday in Bonn. "Whoever throws sand into the gears will end up with nothing."

The U.S. special envoy to Bosnia, Richard Gelbard, said he was "not optimistic" about Poplasen's presidency. He warned Poplasen that naming a fellow hard-liner as prime minister of the Bosnia Serb republic would be a "bad joke" and would send "a powerful negative signal."

"The West needs to put (Poplasen) to the test and put him to the test immediately," said Muhamed Sacirbey, a Muslim political leader who serves as Bosnia's ambassador to the United Nations, in an interview with CNN. "The time for words is over, and it's time now for deeds."

Muslim leader expects NATO will stay through 2000

Joining Radisic in the three-member collective presidency will be incumbent Alija Izetbegovic, the leader of the main Muslim party, the SDA, and Ante Jelavic, of the Croat Democratic Union, who ousted the man currently sitting in the Croat seat, Kresimir Zubank.

On Saturday, Izetbegovic said he expected NATO peacekeeping forces to remain in Bosnia until at least 2000.

"Maybe there will be a reduction of troops, but it will be compensated with quality," Izetbegovic said. He also said he thinks the collective presidency "will function better" with the departure of hard-line Serb Krajisnik.

Reuters contributed to this report.