PENSACOLA NAVAL AIR STATION, Florida (AP) - The US Air Force plans to ground about a third of its active-duty force of combat planes and a top general warned on Tuesday that the branch might not be able to respond immediately to every event when needed.

The Air Force didn't immediately release a list of the specific units and bases that would be affected on Tuesday, but it said it would cover some fighters, bombers and airborne warning and control aircraft in the US, Europe and the Pacific.

General Mike Hostage, commander of Air Combat Command at Joint Base Langley-Eustis in Virginia, said the branch would focus its budget and resources on units supporting major missions, like the war in Afghanistan, while other units stand down on a rotating basis.

"The current situation means we're accepting the risk that combat airpower may not be ready to respond immediately to new contingencies as they occur," Gen Hostage said in a statement.

The sharp budget cuts were triggered on March 1 when Washington failed to reach a deal to rein in deficit spending. The cuts were designed to be so brutal that they would force Democrats and Republicans to reach a deal, but one never happened. That means US$1.2 trillion (S$1.5 trillion) in automatic spending cuts will take effect over the next 10 years if Congress and President Barack Obama don't come up with an alternative.

The Air Force says, on average, aircrews 'lose currency' to fly combat commissions within 90 to 120 days of not flying and that it generally takes 60 to 90 days to conduct the training needed to return aircrews to mission-ready status.

Returning grounded units to mission ready status will require additional funds beyond Air Combat Command's normal budget, according to Air Force Officials.

"Even a six-month stand down of units will have significant long-term, multi-year impacts on our operational readiness," Air Combat Command spokesman Maj. Brandon Lingle wrote in an email to The Associated Press.

For affected units, the Air Force says it will shift its focus to ground training. That includes the use of flight simulators and academic training to maintain basic skills and aircraft knowledge, Lingle said. Aircraft maintainers plan to clear up as much of a backlog of scheduled inspections and maintenance that budgets allow.

On the same day, the US Navy confirmed that the Blue Angels aerobatic team would be cancelling the rest of its season.

Mr Tom Frosch, the Blue Angels lead pilot and team commander, announced the news late Tuesday at the team's Pensacola Naval Air Station headquarters standing in front of the one of the iconic blue-and-gold jets. Frosch said the news marks the first time since the Korean War that the team would not make the air show rounds.

"The Navy held off as long as possible with the hope of salvaging some of the season," Mr Frosch said. "We hope we'll be turned back on for 2014." Most held out hope that the grounding was temporary and that the season could somehow be salvaged.

Thousands of fans flocks to Pensacola Beach each July to watch the team fly over the white sand and turquoise surf. It is always the biggest tourism revenue weekend of the year, said W.A. Buck Lee, president of the Santa Rosa Island Authority. Lee said he had hoped that the six fighter jets would be allowed to continue practicing as a team and the Pensacola Beach show could be replaced by a routine practice over the beach.

Instead, the Navy announced Tuesday that the six elite pilots would maintain only minimum flight hours to remain qualified in their F/A 18 Hornets and that squadron practices would end for the remainder of the season.

"The economic impact of the show for us is more than US$2 million," Mr Lee said. "People are going to start cancelling their hotel rooms and will hurt businesses here."

A spokesman for the Navy said team members would be allowed to fly minimal hours to maintain flight proficiency in the F/A 18 fighter jets, but the six-jet squadron would discontinue group practices for the remainder of the season. The elite pilots selected to serve a two-year rotation with the team are among the top Navy's top fighter pilots. Many are graduates of the Navy's famous Top Gun fighter tactics school.

Mr Forsch said the team will continue its focus on community outreach and on Navy and Marine recruiting.