Congressional negotiators have worked out a deal to allow New Mexico nuclear weapons designers to begin designing a new nuclear weapon to attack underground bunkers.

Sen. Jeff Bingaman, D-N.M., had attempted to block the work. But a compromise will allow the work to begin once defense planners complete a report documenting the need for the weapon, according to Jude McCartin, Bingaman's spokeswoman.

The compromise, first reported last week by the San Jose Mercury News, will allow nuclear weapons designers at Sandia and Los Alamos national laboratories to begin work on the Robust Nuclear Earth Penetrator.

Weaponeers at Lawrence Livermore National Laboratory in California will work on a competing design.

Both teams' designs will be based on modifications to existing nuclear weapons to allow them to slam into the Earth, with their momentum carrying them underground before they explode.

It will be a number of years before any decision is made about whether to actually build the new weapon, McCartin noted, giving time for congressional hearings on the question.

Led by Bingaman, the Senate approved a measure last summer cutting funding for the new weapon, requiring instead that defense planners prepare a report on why it is needed.

The House approved funding for the measure. A conference committee split the difference, requiring the report Bingaman had requested but allowing the work to proceed once the report is completed, according to McCartin.