PITTSBURGH (AP) Halliburton Co. will ask a federal judge for more time to review thousands of pending asbestos claims, the third time the company has sought an extension since agreeing to a settlement worth about $4 billion in December.

Determining the validity of each case, which involves more than 300,000 claimants, has proven to be an enormous task, officials with the Houston-based industrial giant said.

Attorneys for Halliburton were scheduled to appear before U.S. Bankruptcy Judge Judith Fitzgerald in Pittsburgh in late July to ask that a stay, which just expired, be extended until Sept. 30.

Shares of Halliburton fell 71 cents, or 3 percent, to close at $21.59 July 21 on the New York Stock Exchange.

Halliburton agreed to put its DII Industries unit under bankruptcy supervision to help pay the settlement, which includes about $2.8 billion in cash and 59.5 million shares of stock currently worth about $1.3 billion.

The company reported last month that it had supporting evidence for more than half the outstanding claims, and said it expected to complete the review of all outstanding cases by July if victims’ attorneys could provide supporting documentation.

Company spokeswoman Wendy Hall could not say if that information had been provided by those attorneys or how far the review of related documents had progressed since last month.

Phone calls to Perry Weitz, the lead negotiator for the plaintiffs, were not immediately returned.

Halliburton inherited most of the claims four years ago when the oilfield services, engineering and construction conglomerate acquired Dresser Industries Inc. for $7.7 billion.

The case is being heard in Pittsburgh because most of the asbestos claims were filed against a former Dresser subsidiary, Pittsburgh-based Harbison-Walker Refractories Co. That company filed for Chapter 11 bankruptcy last year.

The lawsuits were filed primarily on behalf of people exposed to asbestos while working at plants that produced the material or in places where asbestos was used for fireproofing and insulation, such as steel mills. Inhaling asbestos fibers can cause lung cancer and other deadly respiratory ailments, sometimes decades later.

A lawsuit against Harbison-Walker was filed by Halliburton, which claims that the company promised to take responsibility for all asbestos claims filed against it after 1992. Harbison-Walker ended the practice in 2001.

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