Defiant Serbs Harden Stance : Bosnia: Rebels lay mines to trap U.N. troops, apparently kidnap peacekeeper and intern 10 aid workers. U.N. downplays moves, seeks to restart talks.

Bosnian Serb rebels hardened their defiance of the outside world Tuesday, ordering troops to shoot down NATO warplanes, laying mines to trap U.N. peacekeepers and rebuffing high-level diplomats seeking to rescue abandoned peace talks.

Bosnian government forces clashed with Serbs in the U.N. safe area of Gorazde, but the fighting was reported to be less intense than on the previous day, and the U.N. commander for Bosnia-Herzegovina blamed Muslim-led government units for starting it.

Tensions escalated throughout Bosnia as the Serbs tightened their chokehold on this encircled capital. They also made clear through a coordinated series of retaliations for North Atlantic Treaty Organization air strikes that no foreigners are safe in Serb-held territory.

They warned that the U.N. Protection Force is now considered an enemy.

A Dutch military observer in the Zepa safe area disappeared and was presumed kidnaped when he tried to cross into a Serb-held area. Rebels have also imprisoned 10 workers from a French relief agency at their garrison in the Serb-occupied Sarajevo suburb of Lukavica.

The U.N. commander for Bosnia, British Lt. Gen. Michael Rose, said the incidents were being raised with Bosnian Serb authorities “at the administrative level” but that he did not want the hostile actions to become an issue that would overshadow the broader aim of restarting negotiations.

“I would rather downplay the situation and leave things fairly calm. We are quite capable of existing at the moment, and this is not something I want to take up with them when we have more important things to discuss,” Rose said of the blockade that has effectively made hostages of all U.N. troops, relief workers and foreign journalists in the capital.

Sarajevo’s 380,000 residents were already prisoners of the 2-year-old Serbian siege that has maintained armed checkpoints at all points of entry.

One senior relief official criticized as dangerous the U.N. commander’s posture of ignoring the blockade. “Rose and his people are misleading everyone. They may even be misleading themselves,” said the official, who has spent much of the war in Sarajevo.

In other developments Tuesday:

* President Clinton warned both sides in the Gorazde fighting against improperly interpreting the NATO intervention; he insisted that the Western alliance simply is acting to prod the warring parties to return to peace talks.

* Russian lawmakers and other officials renewed their objections to the NATO action, saying it now imperils Russia’s prospective links with the Western allies.

* The Pentagon disclosed that most of the bombs released over Gorazde on Monday were duds.

* The Belgrade government, accusing them of unfair reporting, said it will bar the Cable News Network and the French news agency Agence France-Presse from reporting in Yugoslavia. The government said it will probably take similar action against other foreign media. CNN said it had not received official notice of the action. But it defended the fairness and objectivity of its reporting. It was unclear what, if any, effect the government statement would have on the news organizations’ reporting from the rump Yugoslavia, which now includes Serbia and Montenegro.

Fear, Defiance

The defiance of Bosnian Serb leaders in their mountain stronghold of Pale, 10 miles to the east, was interpreted by some U.N. and diplomatic sources here as bluster and by others as evidence of fierce resolve.

“We’re in this now, and the only question is whether we’re going to know how to follow through, because the Serbs will keep probing and probing to see where the limits are,” one Western diplomatic source warned. He said he feared the incidents suggested that the rebel leadership is in the hands of military hard-liners who will continue to test the international community’s commitment to halting their deadly land-grab and “ethnic cleansing.”

The Bosnian Serb military commander, Gen. Ratko Mladic, ordered his troops to fire on any NATO planes they consider a threat, Serbian radio in Pale reported.

A Serbian journalist contacted by telephone in Pale described the rebel leadership as confident. He said Mladic and political leader Radovan Karadzic had played a game of chess after visiting a front-line emplacement.

Maj. Rob Annink, a U.N. Protection Force spokesman, described most U.N.-patrolled areas of Bosnia as tense, including Sarajevo. It was the first time the atmosphere in the capital has deteriorated since a Feb. 21 NATO ultimatum that forced Serbs to surrender or pull back the heavy artillery used to batter the city to ruins.

Top U.N. civilian and military officials, as well as U.S. special envoy Charles Redman, had planned to travel to Pale to meet with Karadzic and Mladic to discuss the situation but were told by telephone they were unwelcome, U.N. sources said.

The commander for all 32,000 U.N. troops in the Balkans, French Gen. Bertrand de Lapresle, and the special representative of U.N. Secretary General Boutros Boutros-Ghali, Yasushi Akashi of Japan, flew back to mission headquarters in the Croatian capital of Zagreb after the rebuff.

They left by U.N. helicopter, the only aircraft to risk landing at the Sarajevo airport.

The U.N. humanitarian airlift of food and other supplies to the capital has been suspended indefinitely for security reasons.

Mines, Shells

Serbs laid mines to hamper movement of U.N. troops at the depots where the Serbs’ surrendered tanks and guns are stored, Annink said.

The head of the 50-man U.N. military observer mission for eastern Bosnia, Canadian Maj. Roy Thomas, said about 40 of his men in Serb-held areas were under house arrest by the nationalist rebels and that one Dutch officer had been missing since crossing through a Serbian checkpoint outside Zepa early Monday.

French Cmdr. Eric Chaperon, another U.N. spokesman, said Tuesday that Gorazde was considerably calmer than the previous day, when Serbs pressed in, despite the first NATO air strikes Sunday, to take vast new stretches of government territory along the Drina River in the southeast.

Rose had accused the government forces earlier Tuesday of disrupting the morning calm by firing on Serbs who had moved to within two miles of the city center and conquered several densely populated suburbs.

Chaperon said later that shooting and shelling had come from both sides. “Both of the warring parties were firing at a small hill, which is southeast of the city,” Chaperon said, confirming that the government shooting was directed at rebel forces that had already invaded the enclave.

He said there was no major change in control of territory around Gorazde. About 15% of the U.N. safe area has been occupied by the Serbian nationalists over the past two weeks.

Rose and Lapresle told journalists that the resort to NATO air power was made because U.N. troops were endangered by the Serbian offensive against Gorazde. Eight U.N. liaison officers and five military observers have been deployed to the pocket.

“When my troops get put in a position where they get directly attacked and the only response to preserve life is to use close air support, then it is I that decides that’s what we should do,” Rose said, explaining the sequence of events that led to his calling in air strikes. “There’s no question of it being a political act.”

He described the bombings that destroyed two Serbian artillery positions as “very measured, very controlled, the use of minimum force to preserve the life of my soldiers.”

Lapresle said force had been used “with great restraint and after many warnings.”