* Withdrawal part of complex deal with Assad's forces
* End of rebel presence in heart of "revolution capital"
* Symbolic victory for Assad before expected re-election (Adds detail, background)
BEIRUT, May 7 (Reuters) - Syrian rebels started withdrawing from the heart of Homs city on Wednesday, leaving an early centre of the revolt against President Bashar al-Assad and handing him a symbolic victory less than a month before his likely re-election.
Activists said two buses carrying the first of many hundreds of fighters left the besieged city centre, heading for rebel-held areas of northern Homs province - an evacuation arranged under a deal between insurgents and forces loyal to Assad.
The rebels had held out in the Old City district and several other areas despite being undersupplied, outgunned and subjected to more than a year of siege.
Their evacuation comes after months of gains by Assad's forces, backed by his Lebanese militant ally Hezbollah, along a strategic corridor of territory linking the capital Damascus with Homs and his Alawite heartland on the Mediterranean.
Their final withdrawal from the centre of the city, known as the "capital of the revolution" when protests first erupted against Assad in 2011, would consolidate his military control ahead of a June 3 presidential election.
Assad is widely expected to be the runaway victor in the vote which his opponents have dismissed as a charade.
They say no credible election can be held in a country fractured by ongoing civil war, with swathes of territory outside government control, 6 million people displaced and another 2.5 million refugees abroad.
The Homs evacuation is part of deal between Assad's forces and rebel fighters under which the overwhelmingly Sunni Muslim rebels also agreed to ease their siege of two northern Shi'ite towns, Nubl and al-Zahraa.
The Syrian Observatory for Human Rights said rebels opened the roads to allow aid into the two towns on Wednesday morning at the same time as the first buses collected the departing rebel fighters from Homs.
A total of 1,200 fighters are expected to leave Homs in stages, carefully synchronised with the aid delivery and the release of several captives held by the rebels near Nubl and Zahraa.
Provincial governor Talal Barazi was quoted by state news agency SANA as saying Wednesday's operation would clear Homs of gunmen and weapons, and would be applied across the whole of Homs city.
As well as their stronghold in the Old City neighbourhoods, rebels also still have a presence in the Al-Waer suburb on the city's northwestern outskirts.
More than 150,000 people have died in Syria's civil war. Millions more have fled their homes and the government has lost control of swathes of territory across the north and east. Fighting regularly kills more than 200 people a day. (Reporting by Dominic Evans; Editing by Andrew Heavens)