* PM to outline gas attack intelligence to lawmakers
* Leaked intelligence: Syria has 1,000 tonnes chemical arms
* Officials say France will not act alone in Syria (Adds detail, declassified report)
By Catherine Bremer and John Irish
PARIS, Sept 2 (Reuters) - France's government should not bow to calls from opposition figures to have lawmakers vote on whether to take military action in Syria, the senior government Socialist who heads parliament's foreign affairs committee said on Monday.
President Francois Hollande's demands for Syrian President Bashar al-Assad to be punished for an alleged chemical attack have left him out on a limb since the British parliament voted against carrying out punitive strikes and U.S. President Barack Obama said he would seek Congress approval before any action.
Obama's hesitation was seized upon derisively by Syrian authorities, fighting a two-and-a-half year-old uprising, as a "historic American retreat".
Hollande is the army commander in chief under the French constitution and empowered to order an intervention. His sole obligation is to inform parliament within three days of action starting. Only if it were to last more than four months would he be obliged to seek parliamentary approval for it to continue.
With opinion polls showing up to two-thirds of the public would oppose an intervention in Syria, however, several conservative, centrist and green politicians called over the weekend for France to hold a special parliamentary vote.
"In a complicated situation like this, we need to stick to principles, in other words the constitution, which does not oblige the president to hold a vote, nor even a debate," foreign affairs committee chief Elisabeth Guigou, a veteran of the ruling Socialist Party, told France Info radio.
"I don't see that holding a vote would make any sense politically," she said, noting France would be left in an impossible situation were parliament to vote in favour of action and then the U.S. Congress to vote against.
Interior Minister Manuel Valls also rebuffed the idea of a vote, saying at the weekend the constitution must be respected.
Parliament is due to debate the Syria crisis on Wednesday. Conservative former prime minister Francois Fillon and veteran centrist politician Francois Bayrou were among those who say a vote should also be scheduled.
The last time parliament held such a vote was in 1991 when then-Socialist president Francois Mitterrand sought its support for his decision to join the U.S.-led coalition in the Gulf War.
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Guigou said that doing nothing would send the signal to all authoritarian rulers that using chemical weapons against civilians can go unpunished, but also that France would not act on its own.
"France cannot act alone. To give an intervention legality it would need to be carried out by a broad coalition," she said.
Prime Minister Jean-Marc Ayrault will meet parliament leaders later on Monday to discuss the crisis and share with them French intelligence on the Aug. 21 chemical attack.
Guigou told France Info that French intelligence pointed to Assad's forces being behind the attack, which the United States says killed over 1,400 people, including many children.
A declassified document from French intelligence services, published by weekly newspaper Le Journal du Dimanche, and confirmed as legitimate by a government official, detailed Syria's chemical weapons arsenal, which it said included sarin, VX nerve agent and mustard gas.
The document described Syria's chemical arsenal as one of the world's largest, amounting to 1,000 tonnes, and that Syrian scientists had been developing it since the 1980s to enable Damascus to create an autonomous and massive national production programme.
The agents could all be delivered with either long-range missiles such as SCUDS, aerial bombardments, or short-range artillery, according to the document.
A BVA opinion poll released on Saturday showed 64 percent of respondents opposed taking military action in Syria, 58 percent did not trust Hollande to conduct an operation and 35 percent feared that strikes could "set ablaze" the Middle East. (Reporting by Catherine Bremer and John Irish; Editing by Alison Williams)