By Joseph J. Kolb

ALBUQUERQUE, New Mexico (Reuters) - The Los Alamos National Laboratory is evaluating how to meet a June deadline to permanently discard plutonium-tainted junk in light of a prolonged shutdown of a New Mexico nuclear waste dump after an accident there last month, a lab official said.

Los Alamos, one of the leading U.S. nuclear weapons labs, has been forced to halt shipments of its radioactive refuse some 300 miles across the state to the nation's only underground nuclear repository, the Waste Isolation Pilot Plant, near Carlsbad, according to lab spokesman Matt Nerzig.

The repository has remained closed while the U.S. Department of Energy investigates the origins of a radiation leak that occurred there on February 14, exposing at least 17 workers at the facility to radioactive contamination. It was the first such mishap since the facility opened in 1999.

Nerzig said about 1,000 temporary storage drums of the waste remain at the Los Alamos National Laboratory awaiting shipment to the repository near Carlsbad. The lab faces a strict June 30 deadline to permanently discard of the waste.

"We are determined to complete the campaign on time and meet our obligations to the state of New Mexico," Nerzig said. "Toward that end, we are evaluating options to minimize any adverse impact of the (repository incident)."

The repository is designed as a final disposal site for so-called transuranic waste - discarded machinery, clothing and other items contaminated with plutonium or other radioisotopes heavier than uranium - from government nuclear research and weapons labs around the country.

According to the U.S. Nuclear Regulatory Commission, transuranic waste is mostly a byproduct of recycling spent nuclear fuel or using plutonium to fabricate nuclear weapons.

Los Alamos has been one of the biggest contributors of such waste to the repository, sending thousands of barrels of the radioactive material to the underground site in recent years.

NO WIGGLE ROOM ON DEADLINE

Despite the closure and investigation into the radiation leak at the underground repository, an official with the New Mexico Environmental Department said there will be no wiggle room on the June 30 deadline for permanently disposing of the waste.

"We intend to hold LANL (Los Alamos National Laboratory) to the deadline," said Jim Winchester, communications director, for the New Mexico Environment Department.

Winchester said the lab was working on contingencies to remove the waste from what is referred to as "The Hill" at Los Alamos, but did not elaborate on the options.

Deb Gill, a U.S. Department of Energy spokeswoman, said there was no clear time frame yet for the repository to resume operations, which was dependent on identifying the cause of the leak and completing any required cleanup.

For now, the containers have been stored in a fire-proof structure on a corner of the sprawling lab, 35 miles northwest of state capital Santa Fe, within a campus consisting of 2,000 buildings spread across 36 square miles.

Established during World War Two as part of the top-secret Manhattan Project to build the world's first atomic bomb, the complex remains one of the leading nuclear weapons manufacturing facilities in the United States.

A massive wildfire that raged at the edge of the complex in 2011 burned to within a few miles of a collection of radioactive waste drums temporarily stored at the site. Since then, Energy Department and state officials have made the removal of transuranic waste from the lab to the repository a top environmental priority.

(Reporting by Joseph J. Kolb; Editing by Steve Gorman, Cynthia Johnston and Andrew Hay)