Oct. 17 (Bloomberg) -- Turkish legislators were poised to approve an attack on Kurdish rebels in northern Iraq, a step that may further harm Iraq's security and disrupt oil supplies in the world's third-largest producer.

The parliament in Ankara convened at 3 p.m. today to decide whether to let Prime Minister Recep Tayyip Erdogan authorize a military incursion across Turkey's southern border with Iraq.

Erdogan is threatening to launch an attack against members of the Kurdistan Workers' Party, or PKK, saying U.S.-led forces failed to control about 3,500 militants sheltered in Iraq's north. Washington has warned Turkey to stay out of the Kurdish- controlled region, a relatively calm area of the country.

``The Iraqi government should be given a chance to prevent cross-border terrorist activities,'' Iraqi Vice-President Tareq al-Hashemi said today in Ankara after meeting Erdogan, according to the state-run Anatolia news agency.

The parliament motion, which empowers Erdogan to order one or more military assaults within a year, is supported by his two main political rivals, who have criticized the government in the past for failing to eradicate the threat posed by the PKK.

''Threats are not useful,'' Barham Salih, the Kurdish Deputy Prime Minister of Iraq said in London today. A Turkish raid ''will have serious implications for Iraq, Turkey and for our bilateral relationships. It will not be helpful to anybody,'' he said at a news conference at Chatham House, a consultant that advises European governments on foreign policy.

The PKK, designated a terrorist organization by the U.S. and European Union, has fought the Turkish military for two decades at a cost of almost 40,000 lives, attacking army units and launching bomb attacks in Turkey's cities.

U.S. Warning

The U.S. repeated a warning to Turkey to stay out of Iraq, saying the Turkish army can't crush Kurdish militants by acting alone and must cooperate with Iraq and the U.S.

``The only result of a unilateral action will probably be to allow the PKK to continue to operate,'' State Department spokesman Tom Casey told reporters in Washington yesterday. ``The way to really make progress in the fight against PKK terrorism is for there to be cooperative action.''

Iraqi Prime Minister Nuri al-Maliki phoned Erdogan today to appeal for more time to deal with the PKK, saying Iraqi forces could join the Turkish army in a military operation against the group ``if necessary,'' the CNN Turk television reported.

NATO Urges Calm

Turkey should seek to ``remain calm'' in the face of PKK attacks, North Atlantic Treaty Organization Secretary General Jaap de Hoop Scheffer told President Abdullah Gul in a telephone conversation today, the CNN Turk television reported.

Turkey, with the second-largest army in NATO, sent troops into northern Iraq in pursuit of PKK rebels several times in the decade before the U.S.-led war to oust Saddam Hussein in 2003. It has halted such assaults since the U.S.-led invasion, instead attacking PKK units as they have entered Turkey.

There is a ``common will'' among lawmakers to sanction an incursion, Erdogan said yesterday.

Erdogan's government asked parliament to approve the incursion after more than two dozen soldiers and civilians were killed over the past two weeks in attacks blamed on the PKK.

Turkish companies have started pulling workers out of northern Iraq ahead of today's vote in parliament and the rival Nationalist Action Party urged Erdogan's government to widen the attack on the PKK to include fighters loyal to Iraqi Kurdish leader Massoud Barzani, Vatan newspaper said today.

Crude oil rose above $88 a barrel for the first time in New York yesterday on concerns a Turkish attack may disrupt shipments. Iraq has the world's third-largest oil reserves.

Worsening Relations

Relations between the U.S. and Turkey, both NATO allies, worsened last week after a U.S. House of Representatives committee passed a resolution labeling the World War I-era killing of Armenians by Ottoman Turks as genocide. Turkey withdrew its ambassador to Washington in protest.

At least nine U.S. lawmakers have since withdrawn their support for the resolution. A separate group of Democrats will publicly urge House Speaker Nancy Pelosi today to reconsider her pledge to have the House vote on the resolution before the end of the year.

The Pentagon is drafting plans for alternate supply routes into Iraq in the event Turkey closes its airspace to the U.S. because of the resolution, a senior military official told reporters yesterday.

The U.S. military is ``looking at a broad range of options'' it could pursue if Turkey cuts air and ground access, said Lieutenant General Carter Ham, the director of operations for the Joint Chiefs of Staff, according to the American Forces Press Service. ``That is prudent military planning.''

Seventy percent of U.S. air cargo into Iraq goes through Turkey, including almost all of the new vehicles containing heavy armor to protect against roadside bombs, Defense Secretary Robert Gates said Oct. 11.

A Turkish attack would put the U.S. in a difficult position, Ham said. Turkey is a ``highly valued NATO ally,'' although the U.S. is also committed to Iraq's sovereignty and its right to protect itself, he added.

To contact the reporters on this story: Ed Johnson in Sydney at ejohnson28@bloomberg.net ; Mark Bentley in Ankara at mbentley3@bloomberg.net .