HELENA -- Gov. Judy Martz formally threw her support Tuesday behind a contested biological laboratory envisioned for Rocky Mountain Laboratories in Hamilton and designed to house the most deadly pathogens known.

Martz handed lab officials a signed letter of her support after touring the lab's current facility. It was believed to be the first time any Montana governor has toured the federal lab where Rocky Mountain spotted fever was first identified decades ago and cutting-edge research on chronic wasting disease occurs today.

The lab and its federal overseer, the National Institutes of Health, now want to build a $66.5 million Biosafety Level 4 (BL-4) laboratory at the rural site, with construction beginning as early as the end of this year. BL-4 labs are designed to study deadly diseases for which there is no cure, particularly diseases spread through the air, like the Ebola virus.

The possibility of a new BL-4 sparked controversy both in Hamilton, where some residents worried about their own safety and throughout the nation.

The Hamilton BL-4 is among several other proposed new labs which, if completed, would double the U.S. capacity to work on such deadly organisms. It is also associated with a new push toward protecting the U.S. from biological attack by investigating pathogens that could be used as biological weapons. Some scientists have questioned how thin the line is between defensive biological research and offensive work. They have also questioned the security of such labs against terrorist attack and pushed for more stringent oversight of the scientists working in such places.

But Martz said in a telephone interview Tuesday that she was impressed not only with the Rocky Mountain Labs' scientific history, but also with the environmental study the federal government prepared examining the possible impacts of the proposed new lab.

''These decisions are based on science, not emotion," Martz said. ''They have the scientific background and I think they're pretty confident they're doing the right thing."

Gail Gray, director of the state's Department of Public Health and Human Services, also toured the lab Tuesday, as well as Tom Kindt of the National Institutes of Health.

Marshall Bloom, associate director of laboratory, said Gray also intended to send a letter of support.

The lab is working with the doctors from the state's public health agency to identify what could be a new kind of tick-borne disease found for the first time in the Yellowstone River valley this year.

Rocky Mountain Laboratories already has research labs equipped to handle some deadly organisms like bacillus anthracis, the bug behind anthrax.

Martz said she was impressed that in 80 years, the lab has never had an outbreak and has a good safety record.

Asked about locals who oppose the lab, Martz said that ''there will always be some who will not be satisfied," but that the lab is trying to address all their concerns.

Some members of a local group called Coalition for a Safe Lab have opposed the BL-4 and are asking the federal government to do a more comprehensive study of the lab's effects on Hamilton and its people.

Mary Wulff, a member of the group, said they contacted the governor last year soon after the intended BL-4 was announced. The group has never had a chance to tell Martz their concerns about the lab, which range from an outbreak of deadly pathogens to physical security at the lab.