* Civilians and fighters pinned down by rooftop gunmen
* Rebels caught in a slice of eastern Aleppo
* Snipers can take weeks to dislodge
By Erika Solomon
ALEPPO, Oct 18 (Reuters) - Plucking up his courage, a young boy ducks and darts down a bullet-scarred street in Aleppo, as a rebel with a megaphone shouts directions.
"Don't turn right! Stay left, stay left. Now go, run, run!"
A sniper shot cracks out, and the boy's dangerously bright pink shirt disappears behind a row of charred buses dragged across the road for cover. But the bullet misses, and fighters at the other end of the street burst into cheers.
In Syria's largest city, rebels fighting to topple President Bashar al-Assad have found ways to destroy government tanks and have managed to hold their positions despite attacks by jets and helicopters.
But four months into their campaign to take Aleppo - much of it a jungle of concrete tower blocks - many are pinned down by pro-Assad snipers on the rooftops of the front line and even inside rebel areas.
The local stalemates drag on and on.
"When a sniper sets up in a building, that's it, we could be stuck for weeks trying to find just one guy," said Abu Saif, a 23-year-old rebel in jeans and a camouflage vest.
In late July, rebels armed with assault rifles and homemade rockets fought their way into Aleppo and took control of much of the east of the city in days.
Since then, their advances have been contained by government forces and they have been unable to take the city centre, becoming trapped between the airport east of the city and western neighbourhoods where soldiers and pro-Assad militia are camped out.
Their last offensive, billed beforehand as a "decisive battle", only served to bring the ancient souk and the 8th-century Great Mosque into the fray, without gaining much ground for the anti-Assad fighters.
As rebels guide another civilian past the sniper, a young man watching nearby shakes his head.
"They say they liberate a street. But nowadays, I don't consider it in rebel control if there is a sniper in there," he said, asking not to be named. "If you can't move openly in the areas that are supposed to be yours, you are not free."
Assad's better-armed forces appear to have most of the sniper rifles being used in the war. The rebels too have a few of the high-accuracy weapons, but are mostly armed with assault rifles much less lethal at long range.
A fighter jet gracefully circles over Aleppo before swooping down to bomb a rebel district, unleashing deafening blasts.
There are still eruptions of such full-blown conflict between Assad's forces and the rebels who have been struggling to topple him for more than 19 months.
But increasingly, the war is one of slow attrition.
The Bustan al-Basha district of the city is a wasteland of collapsed apartment blocks where rebels have only advanced a few blocks in recent weeks.
When sniper shots are fired at his bombed-out shelter, fighter Najmeddine carries on puffing on a cigarette as he shoots back with his unit's one anti-aircraft gun.
The fire isn't returned, and he groans and walks away.
"Look at us! This has become a sniper war now, and it is so boring!" he shouts in frustration. His fellow fighters chuckle and stretch out on the blasted sidewalk.
"This is just a sign that this war could take years. It took us weeks to get to this corner from five blocks away," sighs Najmeddine, wiping sweat from his greying moustache and peering around the corner. Snipers nearby have blocked his unit's advance on a security force building for days.
The material cost of rebel advances in neighbourhoods like Bustan al-Basha has been high. Water from burst pipes floods streets littered with shards of concrete and tangles of wires. Entire walls dangle from high corners of shattered buildings.
The human cost has been worse. The major battles here have ended, but civilians and rebels are still gunned down daily by the snipers.
"What's hard about that is that you don't want your fighters to die cheap. W e want to die in battle, not like that," said Ammar, a 34-year-old rebel with scarred and bruised arms. His leg twitches nervously as he shouts at his comrades to stop crossing exposed areas.
Nearby, Najmeddine goes in to take another shot. He has lost two fingers in these back-and-forth gunbattles, but says it hasn't hurt his determination to fight.
"I can still shoot," he says.
Down the road, rebels burn tyres, hoping to obscure a sniper's view and warn civilians away.
But some residents have business too urgent to wait. A bullet-holed pickup truck, with a bleeding man laid in the back, veers around the burning tyres, forcing two rebels to jump out of the way, and speeds across a bridge as gunfire cracks out.
Rebels said they driver might have been trying to get the bleeding man to hospital.
"Did he make it?" a passerby asks the fighters. A gunman stares down the road and shakes his head, replying: "Only God knows." (Editing by Oliver Holmes and Andrew Roche)