Syrian government forces reasserted control of Damascus suburbs on Tuesday after beating back rebels at the capital's gates, ahead of a push at the United Nations for a resolution calling for President Bashar al-Assad to give up powers.

Western and Arab diplomats descended on U.N. headquarters to back a Security Council resolution that would endorse an Arab League call for Assad to delegate powers to his deputy and defuse a 10-month uprising against his family's dynastic rule.

Arab League Secretary-General Nabil Elaraby urged the council to take rapid and decisive action, while Qatari Prime Minister Sheikh Hamad bin Jassim warned the 15-nation body that Syria's killing machine is still at work.

Eleraby made clear that Arab nations are trying to avoid foreign intervention in the Syrian crisis.

The Arab leaders will make the case for the bloc's plan, with U.S. Secretary of State Hillary Clinton, French Foreign Minister Alain Juppe and Britain's William Hague presenting a united western front.

The fate of the resolution depends on whether the Arabs and Western states can get Russia - long Assad's ally - to abstain rather than veto it.

Diplomats have been haggling for days to find a text Moscow will not block, with a main sticking point being the degree to which it expresses support for the Arab plan for Assad to give up powers, U.N. diplomats said under condition of anonymity.

Russia opposes a resolution explicitly backing Arab League calls for Assad to step aside, or which does not rule out the use of force to push him out.

The Western draft Security Council resolution on Syria will not lead to a search for compromise, Interfax quoted Deputy Foreign Minister Gennady Gatilov as saying. Pushing it is a path to civil war.

British Prime Minister David Cameron told parliament: What ... the foreign secretary is doing today with colleagues at the U.N. Security Council is trying to build the strongest possible resolution and say to the Russians: 'Really, if you go on vetoing or preventing these motions, you are going to be completely outside, not just world public opinion, but the very, very clear, expressed opinion of the Arab League themselves.'

BATTLEFRONT

On the battlefront, activists in eastern districts of Damascus said troops fired in the air as they advanced beyond areas from which the defector Free Syrian Army withdrew, capping three days of fighting activists said killed at least 100 people. Tanks also swarmed into the area.

The suburbs are under an unannounced curfew. A small grocery shop opened this morning and soldiers came and beat the owner and forced him to shut down, said an activist in the Ain Tarma neighbourhood on Tuesday.

Others said residents of some eastern districts were allowed to flee their neighbourhoods in vehicles by advancing troops, but that security forces in the district of Irbin had rounded up young men at gunpoint and detained them.

Events on the ground are difficult to confirm as the Syrian government restricts most access by journalists.

Activist groups said 25 people were killed on Monday in Damascus suburbs and dozens more died in other parts of the country, mostly in raids in and around the central city of Homs, which has seen some of the heaviest attacks by Assad's forces.

NEW PHASE

The uprising against Assad - one of the most violent revolts of the Arab Spring - has entered a new phase in recent weeks, with an insurgency whose leadership is based in Turkey daring to show its face at the outskirts of the capital.

A last-ditch bid by Moscow to broker talks between Assad's government and rebels foundered when the opposition refused to attend, citing the continued killing, torture and imprisonment of the president's opponents.

Washington says countries need to accept that Assad's rule is doomed and stop shielding him in the Security Council.

I do not see how he can sustain his rule of Syria, U.S. Director of National Intelligence James Clapper said on Tuesday.

A draft of the U.N. Security Council resolution obtained by Reuters emphasises the need to resolve the current crisis in Syria peacefully and neither authorises the use of force against Assad nor explicitly bars it.

A key sticking point is language in the draft that fully supports the Arab plan, U.N. diplomats said. European delegations were prepared to dilute that language to win over Moscow, while Arab and U.S. delegates were less inclined to compromise, the diplomats said.

One of Russia's leading defence and security think-tanks, CAST, said Moscow could lose billions of dollars in military contracts with Assad if he is pushed aside. Assad's Syria is one of Russia's last allies in the region.

China is expected to join Russia in either vetoing the draft or abstaining to let it pass. So far Moscow has shown little sign of agreeing to allow the resolution, but some Western diplomats say they still hope Moscow will not block it.

U.N. Secretary-General Ban Ki-moon called for consensus among the Council to stop the bloodshed, saying: Every day tens of people are killed ... It is crucially important for the Security Council to act on this.

Syria is the main Arab ally of non-Arab Iran, which has often put Assad at odds with other Arab leaders.

America's plan for Syria is evident and unfortunately some foreign and regional countries take part in America's plans, Iran's IRNA news agency quoted Supreme Leader Ayatollah Ali Khamenei as saying on Tuesday.

REBELS SHOW FACE IN CAPITAL

Assad's forces appear to have decisively beaten back an attempt by the opposition to assert themselves near Damascus.

An activist said armed defectors mounted scattered attacks on government troops who advanced through the district of Saqba, held by rebels just days earlier.

Rebel forays near the capital follow a negotiated victory in Zabadani - a town of 40,000 in mountains near the border with Lebanon - where government forces pulled back under a ceasefire.

Some rebel commanders have spoken of creating liberated territories to force diplomatic action.

Outside the capital, an explosion set fire to a crude oil pipeline feeding an oil refinery in the city of Homs, residents said. A tall plume of smoke rose from the pipeline in farmland east of the refinery, one of two in the country.

Armour-backed troops entered al-Adawiya district in Homs, driving out Free Syrian Army rebels. Residents said tank bombardment and gunfire could be heard across the city in one of the heaviest barrages in weeks, and activists reporting dozens of casualties and field hospitals full of wounded.

The United Nations said in December more than 5,000 people had been killed in the protests and crackdown. Syria says more than 2,000 security force members have been killed by militants.

(Additional reporting by Suleiman al-Khalidi and Steve Gutterman; Writing by Joseph Logan; Editing by Peter Graff and Christopher Wilson)