Britain's defence ministry said about 3,500 military personnel will be available for venue security duties, if needed, compared with 12,200 during the Summer Olympics.
Police numbers will also be trimmed to around 7,000 officers on duty during the Paralympics, Scotland Yard's national Olympic security co-ordinator Chris Allison said Tuesday.
"There is a difference between this operation and the Olympic operation and that is scale," Allison told reporters.
Fighter jets put on standby to intercept threats during the Olympics have returned to normal duties, but the HMS Ocean — the largest ship in the Royal Navy's fleet — will remain berthed in south London to act as a helicopter landing site and logistics base.
Troops have removed surface-to-air missiles installed at six sites around the capital as part of the vast security operation for the July 27-Aug. 12 Olympics, while a wide no-fly zone over east London has been scaled back dramatically. The Civil Aviation Authority said aircraft would now be restricted only from small areas around the Olympics Park, the athletes' village and the Eton Dorney rowing venue in west London.
Security was razor-sharp for the Olympics and officials were relieved it went off without any major security issues.
Britain was America's closest ally in Afghanistan and Iraq, making it a prime target of Islamic terror groups. And dozens of recent terror plots, including the 2006 one to blow up nearly a dozen trans-Atlantic airliners, have been hatched within Britain's sizeable Muslim population, more than 1 million of whom have ties to Pakistan.
Police anticipate that the terror threat level during the Paralympics is "substantial" — meaning a terrorist attack is a strong possibility, Allison said. It is a notch below severe, the level Britain has been at for much of the time since the 2005 suicide bombings when 52 people were killed in attacks on London's transit network.
"We're still obviously prepared for threats to these games, but I think it's fair to say that there is a different degree of risk," said a British security official who spoke on condition of anonymity because he is not authorized to speak to the press.
But the Paralympics present unique problems. Security personnel will have to inspect many of the athletes' specialist equipment, such as wheelchairs or prosthetics, for contraband.
Police and London organizing officials say they are confident guards are prepared for the challenge, and that all participants and visitors will be searched as thoroughly as during the Olympics.
"Our security staff have been trained to deal with the slightly different profile (of people) at the Paralympics," Paul Deighton, the London organizing committee's chief executive, told reporters.
G4S, the private contractor in charge of Olympic and Paralympic security, said it will be able to supply the needed personnel for the upcoming games.
The military had to step in at the last minute before the Olympics when the company admitted it would have a staffing shortfall at the Olympics.
G4S will provide some 5,000 staff to guard the Paralympic games with airport-like security checks.
"We take the task seriously and we're approaching it much the same way as we did the Olympic Games," said Adam Mynott, a G4S spokesman. "Although it's a smaller operation and the scope is smaller, it's still a large sporting event and we don't anticipate any issues."
Associated Press writer Sylvia Hui contributed to this report.