The force receives up to 2,400 criminal record checks per week but is currently processing about 2,300, according to an official report to its strategic crime and policing board.
The Disclosure and Barring Service (DBS) is funded by the Home Office but operated by police forces, to help ensure employers do not recruit people unsuitable to work with children or other vulnerable groups.
The official rules are that 85 percent of applications should be processed in 14 days, 95 percent in 25 days and 100 percent in 60 days.
More than 4,000 people have been waiting over 60 days for West Midlands Police to vet their applications.
The force is performing significantly worse than its counterparts in West Yorkshire and Manchester, the report revealed.
Assistant chief constable Garry Forsyth said: “The force's output is falling below what is expected and it is believed that we increasingly take longer than some forces to research the applicant as our ICT systems grow less reliable and responsive.”
West Midlands currently uses a mix of systems, including its bespoke 'FLINTS' (Force Linked Intelligence System) for crime, an integrated communications and control system from Capita, a proprietary case and custody system from STL Technologies, a command and control system provided by Northgate and Oracle for finance. Vodafone provides mobile voice and data services.
The force awarded Accenture a five-year £25 million contract last July to help improve its use of technology and save money. As part of the contract HP will design a new IT infrastructure focused on supporting 'mobility, security and data analysis'.
West Midlands had to process 6,700 extra checks than expected in the year up to last month, the report explained.
“Last year West Midlands Police received approximately 500 DBS applications daily and cleared around 400 of those. This shortfall has resulted in a backlog,” the force’s information management head Kate Jeffries said.
"This is exceptionally frustrating for those who are awaiting checks and I am extremely sorry for any delay they experience. We are treating the situation very seriously and are working closely with the Disclosure and Baring Service to rectify the situation,” she added.
It is anticipated that West Midlands will have to check 126,500 applications over the next 12 months at a cost of £2 million, £400,000 more than its current budget.
The force insisted it would be able to clear the applications, saying it had taken measures like installing newer, faster computers, increasing broadband bandwidth and recruiting 31 new staff.
However it warned it cannot expect any help with funding from the DBS, which “expects forces to streamline processes and so deliver greater output at no additional cost”.
West Midlands has 8,461 police officers and just over 14,000 employees, making it the second largest police force in the UK after the Metropolitan police.