SARAJEVO, Bosnia-Herzegovina (AP) _ NATO took a tentative step today toward threatening Bosnian Serbs with air strikes over their onslaught at Gorazde, but there was no let-up in the bombardment that has made the town a living hell.

Three rockets hit the town's already damaged hospital, killing at least 10 people and wounding more than 15, U.N. workers said in a message to U.N. offices in Geneva. At least 12 people died in nearby apartment buildings, later reports said.

With Serb artillery lobbying shells into the Muslim town at the rate of one a minute this morning, the few aid workers in Gorazde spoke of despair after a three-week Serb offensive that has killed at least 345 people and wounded more than 1,000.

''This is hell, horror and terror,'' the hospital's director, Dr. Alija Begic, said in a ham-radio transmission monitored in Sarajevo. ''This is not a war anymore. This is slaughter, massacre.''

He said Serb tanks were only about 100 yards away and firing directly into the hospital.

''Please do something that we stay alive. We cannot stand this anymore,'' sobbed another doctor, Aldijana Rebic.

NATO ambassasdors today backed a U.N. request for air strikes to protect U.N.-designated ''safe areas'' like Gorazde, but the alliance delayed a final decision pending military advice on options for using air power.

The allies agreed that ''we have got to find a way to respond positively'' to the request, said Britain's ambassador, Sir John Weston.

U.N. peacekeepers have said it is too late for air strikes around Gorazde because Serb troops are too close in and bombing would endanger the 50,000 civilians estimated to be huddled in the town.

''There is nothing we can do to sustain the fences of Gorazde,'' the U.N. commander, Lt. Gen. Sir Michael Rose, said today.

Aid workers in Gorazde reported Tuesday that the heavy artillery and sniper fire being inflicted on the town was more intense than any suffered in Sarajevo during its siege by Serb troops.

U.N. officials had held out hope for a new cease-fire agreement signed by a Serb leader late Tuesday. But it appeared to be only the latest in a string of broken promises by Serbs to stop the fighting.

Even as Serb guns again pounded the town, the Serbs' political leader, Radovan Karadzic, issued a statement saying: ''The Serbian side unilaterally proclaims peace in Gorazde. With this, the Gorazde crisis comes to an end.''

Karadzic said his declaration was in response to appeals for a cease-fire by President Clinton and Russian President Boris Yeltsin. He also urged other nations to pressure Bosnia's Muslim-led government to return to peace talks.

An International Red Cross official, Vanya Kiwley, said the agency was desperately trying to get a convoy of food and medicine to Gorazde, which is about 35 miles southeast of Sarajevo.

''In Gorazde hospital they are operating without anesthetics, they have run out of analgesics and bandages,'' she said.

The United Nations has been helpless to stop the Serb offensive on Gorazde, and two air attacks by NATO planes last week only infuriated the Serbs. A third attack was thwarted when a British jet was shot down Saturday.

U.N. and aid officials in Gorazde gave harrowing accounts of Tuesday's heavy shelling, which killed 43 people and wounded 112.

A UNHCR doctor in the town described the fear and mayhem in a report to the agency's headquarters in Geneva.

''All of us are chronically frightened,'' the report said.

''We rarely leave the cellar now except to go to the toilet on the first floor. Conditions for the refugees and residents are appalling. They have no food and have to risk their lives to get water,'' it added.

In other developments:

-Serbs released six teams of U.N. military observers who were detained after last week's NATO air strikes at Gorazade, apparently as a deterent to further air attacks. Two teams remained in detention. Some Serb roadblocks around Sarajevo also were re-opened.

-Serb troops returned 18 anti-aircraft guns they seized Tuesday from a U.N. arms depot on Sarajevo's outskirts. The guns were among weapons Serbs gave up in February after a NATO ultimatum to withdraw artillery 12 1/2 miles from Sarajevo or put them under U.N. protection. However, one tank was missing from another collection site.

Bosnian Serbs began the war in April 1992 after a Muslim-Croat vote to secede from Yugoslavia. Armed by the Yugoslav army, the Serbs have seized about 70 percent of Bosnia in fighting that has killed or left missing more than 200,000 people.