A private group that was set to bid on the nation's organ transplant system has decided not to, forcing the government to continue its contentious relationship with the current contractor.

Rand, a Santa Monica, Calif.-based research powerhouse, said the politics surrounding transplant policy persuaded it to withdraw.

"In the current environment, it would be difficult for any new contractor to avoid being perceived as a new combatant in an ongoing power struggle," said the Rand team's letter, which was sent Monday to the Department of Health and Human Services and other interested parties.

The contractor is responsible for developing and maintaining the computer system to match donated organs with patients waiting for them. It also develops rules that determine which patients advance to the top of the list.

The Richmond-based United Network for Organ Sharing (UNOS) has run the transplant system since it was created in 1986. It is operating under a one-year extension.

The network is in the middle of a bitter fight with HHS over who can set transplant policy and what it should be.

HHS wants to break down the geographic lines that govern the current system, in which most organs are offered within defined local and then regional areas, even if sicker patients are waiting just outside the boundaries.

The network says the current system ensures a supply of organs for transplant centers around the country and encourages donation because families know the organs will stay within their communities.

Both sides believe they have the right to set the rules, and Congress has stepped in. It put on hold HHS regulations that directed more organs to the sickest patients.

Congress also is working to rewrite the law that governs transplant policy. A bill passed by the House Commerce Committee would strip HHS of its authority over policy beyond administrative matters and make it virtually impossible for HHS to give the contract to anyone other than UNOS.

HHS and its allies had hoped that Rand's interest in running the system would pressure UNOS to work more closely with HHS.

Rand officials said the organization, a longtime government contractor, is accustomed to dealing with the government on the government's terms, whereas UNOS has its roots as an independent group of transplant surgeons and patients.

But the delays in implementing the HHS rule, the contentious debate in Congress and HHS's delay in issuing a request for contract proposals persuaded Rand to pull out, the group said in its letter.

HHS had no comment.