A long-running effort to allow the import of lower-cost prescription drugs faces a new twist _ President Barack Obama's administration is raising safety concerns that could effectively scuttle it, even though Obama backed the plan as a senator.

Some import supporters question whether the administration is acting to keep the powerful pharmaceutical industry's support for Obama's effort to overhaul the nation's health care system. An administration official denied that.

The Senate debated the import proposal by Sen. Byron Dorgan, D-N.D., on Wednesday as an amendment to Obama's health overhaul legislation. Even before Dorgan introduced it Tuesday evening, the Food and Drug administration sent senators a letter saying the plan would be "logistically challenging" to implement and raises "significant safety concerns."

Dorgan said he was surprised by the letter because Obama co-sponsored Dorgan's proposal in 2007 as a freshman Democratic senator from Illinois. In addition, Dorgan noted, White House Chief of Staff Rahm Emanuel sponsored his own version of the bill that same year as a Democratic House member from Illinois.

Sen. John McCain, R-Ariz., a co-sponsor, accused Obama of reversing his position on the issue and said the administration letter would "certainly impede the ability of Americans to import drugs from Canada."

During his 2008 presidential campaign, Obama said he supported letting Americans buy imported drugs if they were safe and cheaper than in the U.S. The FDA letter restated that support.

As evidence of Obama's continued backing, Linda Douglass, spokeswoman for the White House Office of Health Reform, cited $5 million he proposed in his 2010 budget for the FDA to develop import policies. She said the agency will continue working on ways "to create a pathway to importing safe and effective drugs."

Dorgan's proposal would let U.S. pharmacies and drug wholesalers import FDA-approved drugs from Canada, Europe, Australia, New Zealand and Japan.

Though the amendment has some bipartisan support, it is opposed by lawmakers of both parties from states such as New Jersey that have a heavy drug industry presence. Some participants on both sides concede it will be difficult for Dorgan to win the 60 votes he needs.

Should the plan pass, it could threaten the pharmaceutical industry's support for Obama's health overhaul. Drug companies have been a valuable ally for the overhaul, spending tens of millions of dollars on TV ads backing the legislation. They oppose the drug import proposal.