WASHINGTON — White House officials have blocked a rule aimed at protecting endangered North Atlantic right whales for more than a year by challenging the findings of government scientists, according to documents obtained by the Union of Concerned Scientists.

The documents, which were mailed to the environmental group by an unidentified National Oceanic and Atmospheric Administration official, illuminate a struggle that has raged between the White House and NOAA for more than a year. In February 2007, NOAA issued a final rule aimed at slowing ships traversing some East Coast waters to 10 knots or less during parts of the year to protect the right whales, but the White House has blocked the rule from taking effect.

North Atlantic right whales, whose surviving population numbers fewer than 400, are one of the most endangered species on Earth, and scientists have warned that the loss of just one more pregnant female could doom the species. Some shipping companies have opposed the NOAA proposal, saying slowing their vessels will cost the industry money.

The documents, which House Oversight and Government Reform Committee Chairman Henry Waxman, D-Calif., released Wednesday, show that the White House Council of Economic Advisers and Vice President Cheney’s office repeatedly questioned whether the rule was needed. Waxman, who sent a letter to the White House asking for an explanation, said the exchange “appears to be the latest instance of the White House ignoring scientists and other experts.”

In one document, the Council of Economic Advisers questioned “the reliability of analysis in the published literature on which NOAA is basing its position.” The council conducted its own analysis and concluded that “the relationship between (vessel) speed and (whale) injury … may not be as strong of a relationship as is suggested in published papers.”

NOAA scientists were not swayed, writing in response, “The basic facts remain that (1) there is a direct relationship between speed and death/serious injury, and (2) at vessel speeds at or below 10 knots the probability of death/serious injury is greatly reduced.”

A separate document reveals that Cheney’s staff argued “that we have no evidence (i.e., hard data) that lowering the speeds of ‘large ships’ will actually make a difference.” NOAA again fired back, writing that there was “no basis to overturn our previous conclusion that imposing a speed limit on large vessels would be beneficial to whales.”