WRAPUP 6-West Will End in "dustbin of History", Gaddafi Says

* Gaddafi troops hold ground despite air assault

* Rebels lack leadership, advance bogs down

* U.S., France, Britain agree on NATO role

* Libyan leader defiant

(Adds quotes from battlefield)

By Maria Golovnina and Michael Georgy

TRIPOLI, March 23 (Reuters) - Western powers attacking Libya will end up in the dustbin of history, Muammar Gaddafi said as his troops held back poorly equipped rebel forces despite four nights of coalition air strikes.

While Western air power has grounded Gaddafi's warplanes and pushed back his forces from the brink of rebel stronghold Benghazi, disorganised and poorly equipped insurgents have failed to capitalise on the ground and are pinned down.

The rebels have been unable to dislodge Gaddafi's forces from the key junction of Ajdabiyah in the east, while government tanks are besieging the last big rebel hold-out of Misrata. There is a big risk of stalemate on the ground, analysts say.

At least two explosions were heard in the Libyan capital Tripoli before dawn on Wednesday, Reuters witnesses said. The roar of a warplane was heard above the city followed by a barrage of anti-aircraft gunfire.

"We will not surrender," Gaddafi earlier told supporters forming a human shield to protect him at his Tripoli compound, which came under attack in 1986 from the Reagan administration and once again in the current round of air strikes.

"We will defeat them by any means ... We are ready for the fight, whether it will be a short or a long one ... We will be victorious in the end," he said in a live television broadcast, his first public appearance since the air strikes began.

"This assault ... is by a bunch of fascists who will end up in the dustbin of history," Gaddafi said in a speech followed by fireworks in the Libyan capital as crowds cheered and supporters fired guns into the air.

The Libyan government denies its army is conducting any offensive operations and says troops are only defending themselves when they come under attack.

But rebels and residents say Gaddafi's tanks have kept up their shelling of Misrata in the west, killing 40 people on Monday alone, and also attacked the small town of Zintan near the border with Tunisia.

It was impossible to independently verify the reports.

REBELS BOGGED DOWN

The siege of Misrata, now weeks old, is becoming increasingly desperate, with water cut off for days and food running out, doctors operating on patients in hospital corridors and many of the wounded left untreated or simply turned away.

"The situation in the local hospital is disastrous," said a Misrata doctor in a statement. "The doctors and medical teams are exhausted beyond human physical ability and some of them cannot reach the hospital because of tanks and snipers."

The rebel effort in the desert scrub of east Libya was bogged down outside Ajdabiyah, with no movement on the strategic town since Gaddafi's remaining tanks holed up there after the government's armoured advance along the open road to Benghazi was blown to bits by French air strikes on Saturday night.

Hiding in the sand dunes from the tank fire coming from the town, the rebels are without heavy weapons, leadership, communication, or even a plan. On Tuesday, groups of fighters lounged around, chatting and smoking cigarettes. This was the spearhead of the counter-offensive.

When asked who was in command, one fighter, Mohamed Bhreka, shrugged and said: "Nobody is. We are volunteers. We just come here. There is no plan."

Their heavy machine guns were bolted to the back of pick-up trucks and there was a good supply of assault rifles. But some just had knives or iron bars. Field radios were not to be seen.

Fighters on the frontline of the uprising against Gaddafi's 41-year rule of this oil-producing north African nation said they had lost the heavy weapons needed to take on his tanks.

It remains to be seen whether the rebel's bravado and faith in God are enough to take towns and advance towards their target of capturing Tripoli.

AGREEMENT ON NATO ROLE

Western warplanes have flown more than 300 sorties over Libya and more than 162 Tomahawk cruise missiles have been fired in the United Nations-mandated mission to protect Libyan civilians against government troops.

U.S. President Barack Obama said the allies should be able to announce soon that they have achieved the objective of creating the no-fly zone.

But, he said, Gaddafi would present a potential threat to his people "unless he is willing to step down."

"We will continue to support the efforts to protect the Libyan people. But we will not be in the lead," Obama said.

Obama, facing questions at home about the Libyan mission, duration and cost, wants the United States to give up operational control of enforcing the no-fly zone within days.

Obama spoke with French President Nicolas Sarkozy and British Prime Minister David Cameron on Tuesday and they agreed NATO should play an important role in enforcing the Libyan no-fly zone, the White House said.

France had been against a NATO role for fear of alienating Arab support, while Turkey had also opposed the alliance taking command as it said air strikes had already overstepped what was authorised by the United Nations. But both countries' objections had been overcome, U.S. officials said.

The plan is for NATO's command structure to be used for the operations under the political leadership of a "steering body" made up of Western and Arab nations members of the alliance policing Libya's skies, diplomats said.

French Foreign Minister Alain Juppe said foreign ministers of countries taking part in military action in Libya were set to meet in the coming days to create a clear political structure for operations.

"I've proposed with the agreement of our British colleagues that we set up a political structure to guide operations, involving foreign ministers from countries that are taking part and from the Arab League," Juppe told the French parliament.

EXILE OPTIONS

While Gaddafi scoffed at the West in his latest speech, U.S. Secretary of State Hillary Clinton said the Libyan leader and his allies may be exploring exile options, although it was unclear if he would seriously contemplate stepping aside.

"Some of it is theatre," Clinton told ABC News in an interview, saying Washington was aware of people reaching out "allegedly on Gaddafi's behalf" to try to assess their options.

"A lot of it is just the way he behaves. It's somewhat unpredictable. But some of it, we think, is exploring. You know, what are my options, where could I go, what could I do. And we would encourage that," she said.

Clinton also said the U.S. government had received unconfirmed reports that at least one of Gaddafi's sons may have been killed in air strikes. She said the "evidence is not sufficient" to confirm the reports, but added it was not U.S. forces that would have killed him.

(Reporting by Mohammed Abbas and Angus MacSwan in Benghazi, Maria Golovnina and Michael Georgy in Tripoli, Hamid Ould Ahmed and Christian Lowe in Algiers, Tom Perry in Cairo; David Brunnstrom in Brussels, Phil Stewart in Moscow, Andrew Quinn in Washington; Writing by Peter Millership; Editing by Giles Elgood)