(Adds link to scenarios factbox, copy unchanged) (Releads with police braced for violence)

By Chalathip Thirasoonthrakul

BANGKOK, Nov 21 (Reuters) - Thai police are braced for violence at an anti-government rally this weekend and have asked the army for reinforcements to prevent a repeat of last month's bloody street battles, a senior officer said on Friday.

Leaders of the People's Alliance for Democracy (PAD) have called for a demonstration at parliament on Sunday to oust the government, which it blames for a grenade attack on their Bangkok protest site on Thursday that killed one person and wounded 23.

"Judging from the tone of their speech, they want to incite violence and we will have to find ways to avoid it," Major General Anan Srihiran of the Metropolitan Police Bureau told Reuters.

The PAD accuse the government of having a hand in Thursday's grenade attack. Prime Minister Somchai Wongsawat, whom the PAD accuse of being a puppet for exiled leader Thaksin Shinawatra, has denied any involvement.

Anan said police had not finalised the number of officers to be deployed but they will be equipped with water cannon and tear gas. The army, navy and air force had agreed to send 3,000 "riot troops" to help out on Sunday and Monday, he added.

In October, two people were killed and hundreds wounded, including scores of police, in fighting that erupted as police fired tear gas to remove protesters trying to stop Somchai delivering his maiden speech to parliament.

Major bloodshed would raise the chances of a military coup only two years after the army's removal of Thaksin, although army chief Anupong Paochinda has said repeatedly a putsch would do nothing to resolve Thailand's political rifts. (For a related scenarios factbox, please click on [ID:nBKK398096])

The PAD enjoy the backing of Bangkok's urban middle classes and elite, including Queen Sirikit, while Thaksin and the government claim their support from the rural voters that returned a pro-Thaksin party in a December election.

STRIKE THREAT

Upping the pressure on Somchai, public sector unions called for a nationwide strike on Tuesday unless he stands aside, a threat that, if carried out, would deepen the economic impact of a political crisis now in its fourth year.

Government decision-making has ground to a halt, intensifying fears about the export-driven economy's ability to withstand a global recession. Year-on-year exports rose just 5.2 percent in October compared with 19.4 percent in September, Commerce Ministry data showed on Friday.

"If the government remains on Nov. 25, we will strike," Sawit Kaewvan, head of an umbrella group representing 200,000 workers at 43 state enterprises, told reporters.

In August, a partial strike by unions in support of the PAD caused havoc on the roads and railways, delaying shipments of commodities ranging from crude oil to rubber.

Sawit also called on union members to attend Monday's rally at parliament, where MPs are debating legislation relating to next month's regional summit to be hosted in the northern city of Chiang Mai.

House leaders said they were not prepared to move the session to a new venue, setting up a potentially serious confrontation.

"We are talking about the pride and dignity of parliament and the country," Deputy House Speaker Apiwan Wiriyachai told a Bangkok radio station.

The PAD have managed to muster crowds in the tens of thousands this year, although their numbers at Government House, which they have occupied permanently since August, have been dwindling.

Even if Monday passes off without incident, tensions are likely to remain high with Thaksin -- now in exile having skipped bail in a corruption case -- set to address a mass rally of supporters around Dec. 13. (Writing by Ed Cropley; Editing by Darren Schuettler and Paul Tait)

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