Skirmishes Flare as Clock Ticks to Bosnia Truce : Balkans: Limited fighting is reported. U.N. engineers race to restore power to Sarajevo.

ZAGREB, Croatia —  Warring sides maneuvered for position Friday in northwest Bosnia-Herzegovina as U.N. engineers scurried to restore utilities to the capital, Sarajevo, in advance of a cease-fire expected to begin Tuesday.

U.N. officials said as many as 600 Croatian army soldiers had crossed the Bosnian border near the northwestern town of Bihac to back up Bosnian government troops repelling attacks by Bosnian Serbs.

Military analysts said the movement was meant to dissuade the rebel Serbs from launching a major offensive in anticipation of the upcoming cease-fire.

U.N. spokesman Chris Gunness said it did not appear that either side had begun a push for new territory.

“There has not been the upswing in fighting that some had predicted,” Gunness said. “It has been fairly quiet all day.”

Western diplomats said both sides have been pressured to limit military actions so that the cease-fire does not unravel even before it begins.

President Clinton announced Thursday that the warring parties had agreed to stop fighting at 12:01 a.m. Tuesday if certain conditions are met. Previous cease-fires in Bosnia--there have been 35, according to the United Nations--have been preceded by last-minute rushes for territory.

“Any major flurry of activity on the battlefield would likely change the balance in some sensitive areas and could undermine the entire agreement,” a Western diplomat said in Zagreb, the Croatian capital. “Everything is being done to make sure that does not happen.”

As a key condition for the cease-fire, electricity and natural gas supplies to Sarajevo must be restored in full before Tuesday. The utilities have been operating sporadically throughout the 42-month-old war but have been largely out of service since April, when the last cease-fire collapsed.

Officials from the Office of the U.N. Special Coordinator, which has been charged with restoring essential services in the Bosnian capital since March, 1994, said they expect to meet the deadline. If it is not met, the cease-fire will be put off until the utilities are operating.

Stephen Bowen, chief of staff to Special Coordinator William Eagleton, said all sides--the Bosnian government, Bosnian Croats and Bosnian Serbs--are cooperating with U.N. efforts to repair downed utility lines and gas pipelines but that there is substantial damage.

“It is going to be very difficult to meet the deadline,” Bowen said. “But with continued cooperation of all parties, we still expect to meet the conditions set by the cease-fire agreement.”

Natural gas from Russia is expected to begin flowing at the Hungarian border with rump Yugoslavia this morning en route to Sarajevo.

U.N. engineers said it will take several days to check the safety of the pipeline and for the gas to actually reach the capital city.

*

Engineers said the biggest problem involves restoring electricity. Power lines--half a mile long--have been downed in an area that is heavily mined by Bosnian Croat forces and inaccessible to repair crews.

Military experts estimate that there are 3 million mines in Bosnia, many in the Sarajevo area. Mine clearing is a tedious and painfully slow process, with work sometimes progressing at a pace of one square yard per hour. But with Bosnian Croat help in locating the mines, officials said the half-mile stretch could be cleared over the weekend.

“The Bosnian Croats have records and maps of their own minefields,” said Bob Keeley, a bomb disposal adviser to the United Nations. “I suspect rather than us going in, we will ask them. Their progress rate would be much faster than ours.”

Gunness, the U.N. spokesman, said the organization is optimistic that the cease-fire will begin on schedule and that it will set the stage for a more permanent peace settlement.

“There may again be problems of mines in areas the U.N. is going to be expected to patrol,” he said. “I don’t think we should underestimate the practical problems that now confront us. But we hope the commitments the parties have given, unlike the 35 other cease-fires that they have committed themselves to, they are now going to respect.”

*

Some observers, however, were less optimistic that this truce will be any different.

One Western diplomat said the Bosnian government, which has enjoyed tremendous military success in recent weeks, is not convinced that it will get a better deal at the negotiating table than on the battlefield.

“We have been trying to hammer them into compliance, but the time is not yet ripe,” the diplomat said. “They don’t believe they have taken enough territory to dictate the terms of a peace settlement. Until then, the prospects for peace in Bosnia are not very good.”

If the truce does take hold, international peacekeeping units might be asked to establish “areas of separation”--demilitarized zones--between the Bosnian government and rebel Serbs, senior officials of the North Atlantic Treaty Organization said Friday.

Ending a meeting in Williamsburg, Va., NATO defense ministers also agreed to invite Russia to participate in the peacekeeping operation.

Both U.S. and foreign officials said the NATO allies are divided over a side issue in the peacekeeping effort--a proposal by Defense Secretary William J. Perry to provide military training to Bosnian government troops to help strike a military balance between the government and the Serbs.

Although France and some other countries oppose the plan, other delegations--particularly the British--said it might be necessary.

At the same time, Perry told reporters that he is considering proposing that the job of “professionalizing” the Bosnian army be contracted out to a private consortium, as has been done with the Croatian army, whose training is being overseen by a team of retired U.S. generals.

Times staff writer Art Pine in Williamsburg contributed to this report.