By Katharine Houreld

ISLAMABAD (Reuters) - Saudi Arabia has asked Pakistan for military aircraft, warships and soldiers, Pakistani Defence Minister Khawaja Asif said on Monday, at the start of a parliamentary debate on whether Pakistan should get involved in a Saudi-led campaign in Yemen.

Saudi Arabia, the Gulf's main Sunni Muslim power, has asked Sunni-majority Pakistan to join a Saudi-led military coalition that began conducting air strikes last month against largely Shi'ite Houthi forces in Yemen.

Prime Minister Nawaz Sharif has hedged his bets. He has repeatedly said he will defend any threat to Saudi Arabia's "territorial integrity" without defining what threat, or what action.

"Saudi Arabia has asked for combat planes, warships and soldiers," Asif said, without specifying where Saudi wanted them deployed.

Arif Rafiq, a Washington-based adjunct scholar with the Middle East Institute, said earlier Pakistan was hoping to satisfy Saudi expectations at a "minimal" level.

"They're unlikely to be part of any meaningful action inside Yemen," he told Reuters. "Maybe they will reinforce the border."

Sharif owes the Saudis. Endemic tax dodging means Pakistan needs regular injections of foreign cash to avoid economic meltdown. Last year, the Saudis gave Pakistan $1.5 billion. Saudi Arabia also sheltered Sharif after he was overthrown in a 1999 military coup.

But joining the Saudi-led coalition could inflame a sectarian conflict at home where about a fifth of the population is Shi'ite and attacks on Shi'ites are increasing, further destabilizing the nuclear-armed nation of 180 million people.

Pakistani intervention would probably also anger Shi'ite power Iran, which shares a long and porous border in a region roiling with its own separatist insurgency.

Pakistan's other main borders are with arch enemy India and Afghanistan, where Pakistani troops are conducting anti-militant operations. The Iranian foreign minister will visit Pakistan this week.

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In the debate on Monday, Aitzaz Ahsan, Senate leader of opposition, demanded Sharif clarify his comments.

"What does [defense minister] Khawaja Asif mean by the violation of sovereignty of Saudi Arabia and the strong response from Pakistan?" he asked. "If the government wants to send troops to Yemen or Saudi Arabia, what will their exact mandate be?"

The session also saw stormy scenes as a major opposition party, the Pakistan Tehreek-e-Insaf, ended a seven-month long boycott of parliament.

PTI boycotted parliament and occupied part of the capital during months-long street protests last year over alleged election rigging. They are firmly opposed to sending troops.

NOT SAUDI'S HANDMAIDEN

Pakistan has a long record of contributing troops to U.N. peacekeeping missions but public opinion seems largely against intervention in any Saudi-led action in Yemen.

"Pakistan is not Saudi Arabia's handmaiden, doing its bidding at the flick of a wrist," the Express Tribune said in an editorial.

Many analysts say the military, which has ruled Pakistan for more than half its existence since independence, has the final call. The generals have been silent.

Pakistan has nearly 1.5 million active soldiers and reserves, but about a third of those are tied up with operations along the Afghan border. The bulk of the remaining forces face off with nuclear-armed India. Others are executing the government's new counter-terrorism plan.

Even though Saudi Arabia is a "special friend" of both the government and the military, Pakistani intervention in Yemen might be unwise, said retired Major General Mahmud Ali Durrani, a former national security adviser.

"If it was to defend Saudi Arabia against aggression, in spite of our commitments, I think we would stretch to sending troops," he said. "To send our troops to a third country - I think that would be foolhardy.

"Either way, it is an absolutely terrible choice to be made for Pakistan."

(The story adds full name and title of Sharif in paragraph 2)

(Additional reporting by Mehreen Zahra-Malik and Syed Raza Hassan; Editing by Nick Macfie, Robert Birsel and Giles Elgood)