WASHINGTON - The U.S. Forest Service has again missed its deadline to complete studies needed to shape the agency's future aerial firefighting strategy, igniting concern from a California lawmaker as wildfire season intensifies across the Inland area.

The Forest Service's director of fire and aviation, Tom Harbour, acknowledged Friday that some of the review work initially scheduled to be complete in January won't be finished until next year. Harbour attributed the delays to the complexity and high stakes -- both in terms of cost and human lives -- involved with modernizing the federal aerial firefighting fleet and accompanying policies.

He stressed that plenty of resources are on hand to battle flames in Inland Southern California, where several blazes have ignited in recent days, including a wildfire Friday in the Cajon Pass that shut down Interstate 15.

"This fall in SoCal, we've got more than enough stuff to cover the fire needs," Harbour said.

For example, he said, three CL 215 firefighting planes known as "Scoopers," able to drop hundreds of gallons of water at a time on flames in remote areas, were brought to the San Bernardino National Forest during a recent blaze.

But Sen. Dianne Feinstein, who first raised concerns about the delays in February, said she remains unsatisfied with the agency's progress and said she plans to seek answers from Harbour's boss.

"Fire season has begun in California, and millions of acres are at high risk of wildfire," said Feinstein, D-Calif. "I intend to meet with Forest Service chief Tom Tidwell to understand why they have again failed to meet this deadline and enact a strategy to protect Californians from wildfires in the coming years."

In May 2010, Tidwell told a Senate subcommittee that the agency was on track to complete by January this year reviews of nighttime aerial firefighting operations and the optimal mix of air tankers and helicopters in the national fleet.

A separate large air tanker strategy, meant to guide the Forest Service's acquisition of water-dropping planes in the years to come, also was due to be finalized in January.

When none was completed, Feinstein pressed for answers from U.S. Agriculture Secretary Tom Vilsack, who oversees the Forest Service. At the time, Vilsack said all three were expected to be finished by the end of summer. Harbour echoed that statement in a June interview.

On Friday, Harbour said the reviews still were not done, slowed by the sheer complexity involved in overhauling the nation's aerial firefighting fleet and policies.

The nighttime helicopter study is focused solely on Southern California's forests, which are home to thousands of people and perennially at risk of wildfire. Because of safety concerns, the Forest Service gave up night helicopter missions in the 1980s.

Officials are considering a return to the practice. But they have identified some 130 separate "risk items," including the protection of crews in the air and people on the ground, that must be addressed before the study is complete, Harbour said.

The RAND Corporation, on behalf of the Forest Service, is conducting the study to determine the best mix of firefighting planes and helicopters. Estimated completion of that study has been pushed to early 2012, a year after it was expected. The large air tanker study could be finished by early fall, Harbour said.

Together, Harbour said, the three studies will be used to formulate important policies meant to protect firefighters and those they protect. And a modernized fleet of firefighting aircraft will cost hundreds of millions over the next two decades.

"Given the magnitude of that kind of investment -- that's why we're trying to take this so very careful," he said. "We're very sensitive to the commitment that the chief and the secretary have made, and we're working just as fast as we can."