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By Zeeshan Haider

ISLAMABAD, Feb 7 (Reuters) - Pakistani authorities announced two "important arrests" in the assassination of opposition leader Benazir Bhutto on Thursday, as her husband issued a rallying call to supporters ahead of an election his wife should have fought.

Polling was put off until Feb. 18 after the slaying of the most charismatic Pakistani politician of the past 20 years sucked oxygen out of campaigning and heightened international concern about mounting insecurity in the nuclear-armed country.

The arrests were made in the garrison city of Rawalpindi, where two-time prime minister Bhutto was killed in a gun and suicide bomb attack by a hit team Pakistani and U.S. intelligence believes was sent by a Taliban commander linked to al Qaeda.

"These are important arrests. Investigations are under way," Interior Ministry spokesman Javed Iqbal Cheema said.

A senior police officer in Rawalpindi identified the suspects as Hasnain and Rifaqat, but gave no other details. The arrests follow two last month, including a 15-year-old youth who admitted being a back-up suicide bomber.

Conspiracy theories still swirl over who was behind the gun and suicide bomb attack that killed Bhutto.

Controversy also rages over whether Bhutto was killed by a bullet or by a concussive head injury caused by the bomb detonated after an assassin shot at her from close range.

A poll conducted by Gallup Pakistan found that almost half of all Pakistanis believe government agencies or politicians allied to President Pervez Musharraf were involved in the assassination.

A British police team that the government invited to investigate is expected to share its findings with Pakistani investigators in the coming days.

While not a presidential election, the outcome could have serious consequences for U.S. ally Musharraf, who came to power as a general in a coup in 1999 and is now going through his most unpopular period.

Musharraf could face impeachment if a hostile parliament emerges from the next parliament.

FIGHTING TALK

Bhutto's widower Asif Ali Zardari, in a speech to thousands of mourners gathered to mark the end of a 40-day Muslim mourning period at his wife's ancestral village in southern Sindh province, vowed to risk assassination championing her cause.

"If I am martyred before completing the mission of Benazir Bhutto, then I should also be buried here," Zardari said in a speech televised by private news channels.

"This is the fight between establishment and the people," said Zardari, who spent eight years in jail but was never convicted of corruption charges he says were politically motivated.

Zardari, who a day earlier scotched talk that he wanted to become prime minister, has not said whether he favoured working with or against Musharraf should the Pakistan People's Party ride a wave of sympathy to victory in the vote later this month.

About 20,000 people gathered in Garhi Khuda Baksh to pay their last respects, and chants of Koranic verses and sombre hymns filled the chilly morning air in the dusty village set amid paddy fields in a rural backwater of southern Sindh province.

Hordes of people forced their way inside the white marble mausoleum chanting "Long Live Bhutto", some weeping and beating their heads in grief, before Zardari was able to pray at the grave, strewn with rose petals, where Bhutto lies alongside her father.

Zulfikar Ali Bhutto, Pakistan's first popularly elected prime minister, was toppled and hanged by the military in the late 1970s, but the PPP still draws on his populist appeal.

The PPP named Bhutto's 19-year-old son, Bilawal Bhutto Zardari as party chairman and Zardari as co-chairman, in accordance with a will Bhutto wrote just before she returned to Pakistan in October, eight years after being hounded out.

An Oxford University student, Bilawal, has said he planned to pursue his mother's legacy after completing his studies. Neither he nor his two sisters were at the graveside on Thursday. (Additional reporting by Faisal Aziz in Garhi Khuda Baksh; Writing by Simon Cameron-Moore; Editing by Bill Tarrant)

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