* Government says deal is insignificant
* Country facing economic crisis
* Small protests have erupted over the last few weeks
By Alexander Dziadosz
KHARTOUM, July 4 (Reuters) - Sudan's main opposition parties on Wednesday called for strikes, sit-ins and demonstrations to topple the government of President Omar Hassan al-Bashir, throwing their weight behind anti-austerity protests.
The Arab-African country has been mired in an economic crisis since oil-producing South Sudan seceded a year ago, and tough spending cuts aimed at plugging a budget gap prompted protests across the country about two and a half weeks ago.
Opposition parties, struggling with an image as fractious and ineffective, had so far only voiced limited support for the demonstrations, which have rarely mustered more than a few hundred people at a time.
Large demonstrations have been relatively rare in Sudan, which has so far avoided the "Arab Spring" protest movements in Egypt and Libya. Security forces usually quickly disperse protests.
The main opposition groups on Wednesday signed a pact calling for "collective, peaceful political struggle in all its forms... to overthrow the regime" including "strikes, peaceful demonstrations, sit-ins and civil disobedience".
Supporters outside the National Unionist Party's Office in the Khartoum suburb of Omdurman, chanted "revolution, revolution until victory", before the deal was signed.
Farouk Abu Issa, head of the National Consensus Forces, an umbrella group of opposition parties, said the deal - which vowed to carry out a "democratic alternative programme" after the current government fell - would fuel more demonstrations.
"We want to rally our people, organise our people so that they stand fast with us in achieving our goal in toppling this regime," he told Reuters after the deal was signed.
It was not clear when the opposition leaders planned to bring their members to the streets in force, but activists have called for more demonstrations on Friday.
GOVERNMENT PLAYS DOWN PROTESTS
If Bashir - in power since a bloodless 1989 coup - and his ruling National Congress Party were deposed, a ceasefire would be declared on all fronts against the multiple armed insurgencies Sudan is facing, the document said.
The parties also agreed to cancel laws restricting freedoms, hold a national constitutional conference, prepare the country for free elections and carry out a variety of other reforms.
The government already fighting armed insurgencies in its western Darfur region and in two southern border states, has played down the protests.
Information Ministry official Rabie Abdelati said the opposition parties did not have the popular momentum to turn their vows into action. "They have no support from the people," he said. "We are not bothering about what they are saying."
The opposition leaders who signed the deal included Hassan al-Turabi, head of the Popular Congress Party, who was once one of the most powerful figures in Sudanese politics but whose influence has declined since he fell out with Bashir in the late 90s.
They also included the general secretary of the Umma party, whose leader Sadeq al-Mahdi was elected premier in 1986 after mass protests, mainly against food inflation, ousted the country's military ruler a year earlier.
Student activists have mostly led Sudan's recent protests, trying to use discontent over soaring food and other prices to build a broader movement to topple the government and make the political system more democratic.
Officials have dismissed the demonstrations as the work of a handful of agitators whose aims are not shared by the majority of Sudanese and blamed "Zionist institutions" for stoking the unrest.