The force answered just two in five calls to its 101 service within the target time of three minutes in June, according to a report to the West Midlands Police and Crime Commissioner's strategic board.
It means the force was given a poor grading for service standards in its citizen charter, although its response to 999 emergency calls over the same period was rated "good".
Police chiefs put the failing down to a "significant increase" in demand, which has seen the average number of daily calls for all services surge past 6,000.
Police and crime commissioner Simon Foster has vowed to focus on ensuring the West Midlands public gets "the service they need and are entitled to expect".
The report said: "Following the lifting of Step 3 Covid-19 restrictions on May 17 coinciding with a spell of warm seasonal weather, the West Midlands, as well as the whole of country, has seen a significant increase in demand.
"This has translated to calls for service, as measured by volumes of 999 calls and 101 calls, as well as live chat that have regularly passed 6,000 records a day.
"This number is similar to the peak pre Covid-19, but has continued for a period of at least a month at the time of writing."
The report adds: "May 2021 was the first month more calls were received on the emergency channel rather than non-emergency. This level of demand has put pressure on service levels in terms of timeliness of answering the demand channels.
"The priority is always to answer emergency calls and resource is dynamically moved to ensure this channel is prioritised, however this has meant wait times for 101 and live chat have been outside those of the service standards in our citizen charter.
"For May, 56 per cent of 101 calls were answered within the three minute service standard and currently (June) 40 per cent, hence the red poor grading versus the performance framework."
Mr Foster said waiting times for non-emergencies had been impacted due to police prioritising emergency calls.
"This is an area I will be focusing on to ensure the public gets the service they need and are entitled to expect," he added.