* Activists say at least 80 dead in past 36 hours
* Damascus puts overall death toll at 6,044
* Homs quarter bombarded for 17 days
* U.N. advance peace-monitoring team due in Syria
By Dominic Evans
BEIRUT, April 4 (Reuters) - Syrian opposition activists accused forces loyal to President Bashar al-Assad of bombarding rebel areas on Wednesday as a U.N. mission was expected to arrive in Damascus in a first step to implement an international peace plan.
Activists said at least 80 people have been killed since Tuesday despite the imminent arrival of the advance team from the U.N. peacekeeping department.
The advance mission is part of the latest international effort to end a year of bloodshed that began with peaceful protests against Assad's authoritarian rule in March 2011.
Activists said troops and police loyal to Assad pressed on with a campaign of raids and arrests in rebel areas, accompanied by bombardments, gun battles and sniper attacks.
"Since this morning they have been shelling Khalidiya neighbourhood, that is in its 17th day," said Hadi Abdullah by telephone from Homs, the city of one million which has suffered most in the bloody 12 month uprising.
"Whatever it is that hits the area leaves a horrible sulfur smell, like rotten eggs."
Human rights group Amnesty International said it had counted 232 deaths since Syria accepted Annan's plan on March 27.
Assad's government issued its latest official death toll for the 12-month uprising. It told the United Nations that 6,044 people had beeen killed of whom 2,566 were soldiers and police.
The United Nations itself says Assad's forces have killed more than 9,000 people in the past year.
The mission, headed by Norwegian General Robert Mood, is part of efforts to implement a deal between Assad and international mediator Kofi Annan for an April 10 withdrawal of Syrian forces, to be followed by a ceasefire by rebel forces within 48 hours.
During the visit, it is expected to discuss deploying some 250 U.N. monitors to oversee a ceasefire. But his acceptance of a troop withdrawal has met scepticism among the Syrian opposition and its Western and Arab supporters.
"The Syrian authorities have said they will do that by April 10," British Foreign Secretary William Hague said in London.
"There is no sign of them doing it so far. Attacks on the citizens, the civilians of their country have continued, the murder, oppression, and torture of the regime has continued..."
U.S. ambassador to the United Nations Susan Rice said on Tuesday the Security Council would have to respond if Assad used the next seven days to intensify the violence.
Syria's ally Russia however attacked the "Friends of Syria" group of Western and Arab nations who met in Istanbul at the weekend, saying it was undermining Annan's peace mission.
"Everyone has supported Kofi Annan's plan, but decisions at the 'Friends of Syria' group meeting aimed at arming the opposition and at new sanctions undermine peace efforts," state-run Itar-Tass quoted Foreign Minister Sergei Lavrov as saying.
Despite its pro-Assad tone, some diplomats have said Moscow has grown increasingly frustrated with Damascus and its failure to end the uprising.
"Russia believes regime change in Syria would result in an Islamist regime after a great deal of bloodshed," one senior diplomat told Reuters.
Syrian Foreign Minister Walid al-Moualem is due in Moscow for talks on April 10, Russia's Foreign ministry said.
The opposition Syrian Observatory for Human Rights, a British-based monitor which collates reports from inside Syria, said 58 civilians and 18 soldiers were killed on Tuesday.
It said 20 civilians died in Homs province, including 15 killed in bombardment, shooting and sniper fire in Homs city.
In Idlib province, 20 civilians and seven soldiers were killed in clashes in Taftanaz village, east of Idlib city. Rami Abdulrahman, head of the SOHR, said rebel fighters had hit at least two of the tanks bombarding the village.
In Homs province on Wednesday, seven people were killed during clashes, the Observatory reported.
The Syrian state news agency SANA said "several terrorists" and three security men were killed in Taftanaz. "Armed terrorist groups ... were attacking citizens, and perpetrating acts of killing, kidnapping and planting explosives," it said.
"At a poultry farm in a Dir Baalba orchard (Homs province), the terrorists killed a number of citizens in cold blood, mutilating and burning their bodies after kidnapping them. The terrorists also killed four women at one house in the same neighbourhood after storming it," SANA said.
Accounts of the violence could not be verified because Syria's government restricts access to independent journalists.
Some analysts predict that huge numbers of Syrians would fill the streets to demand Assad's resignation if the threat of armed repression were lifted. "Millions will start demonstrating and Assad can't afford to see this," said Randa Slim, from the Middle East Institute in Washington.
A video said to have been filmed in Damascus on Tuesday night showed a line of fire, probably from burning tyres, cutting off six lanes of traffic on a downtown expressway.
In the Barzeh district of central Damascus, a device exploded in a car belonging to a man close to the authorities and in Beit Saham outside the capital three people were killed and more than 15 wounded by an explosion, activist reports said.