His Majesty's Inspectorate of Constabulary and Fire & Rescue Services (HMICFRS) said the force's work was "inadequate" in these three areas and was not able to "effectively meet the demands" of some of the work.
The findings were published three months after the force was put into special measures by the watchdog when it was found it had "issues about how it identifies and assesses vulnerability" and "needs to carry out more effective investigations and improve victim support."
In the latest inspection, Staffordshire was also graded as requiring improvement in five areas: its treatment of the public; because it was "missing opportunities" to protect vulnerable people; over how it records data about crime; as well as needing to do better in developing a positive workplace; and making a good use of resources.
It was only found to be adequate in one area of work.
Inspector of Constabulary Wendy Williams said: "I have serious concerns about Staffordshire Police's performance in responding to the public, investigating crime and managing its offenders and suspects. The force needs to improve in these areas as a matter of urgency to keep the public safe.
"It is missing opportunities to identify and safeguard vulnerable people and needs to improve how it provides advice about preventing crime and preserving evidence when taking calls from the public.
"The force's investigations need to improve through proper planning, regular supervision and following the Code of Practice for Victims of Crime. At present, it doesn't always properly support victims, accurately assess their needs or pursue evidence-led prosecutions where appropriate.
"Staffordshire Police also needs to improve how it monitors known offenders and outstanding suspects. At present, it isn't able to effectively meet the demands of this work."
The force will continue to be subject to so-called enhanced monitoring by HMICFRS as part of the engagement process, known as being put into special measures.
Ms Williams said: "I am reassured by the force's proactive response to our inspection and so far during our monitoring process. The force has developed robust plans to improve, which are in the process of being introduced, and we are beginning to see positive signs in some areas. This approach allows for cautious optimism, and I will continue to closely monitor the force's progress."
Chief Constable Chris Noble, who took charge of the force in December, said he "fully" accepts the findings of the report and is "committed to addressing its recommendations", adding: "We are already well under way with these improvements, a fact recognised by the Inspectorate.
"This report will be concerning for Staffordshire residents but we have specific and clear plans to deliver the standard of service our communities expect and deserve. This will not be an easy journey and it will take time to embed and fully realise improvements - but it is one I and my staff are fully committed to."
Staffordshire's police and crime commissioner Ben Adams said: "There is still work to be done to bring some fundamental police services up to the standards people expect and deserve. I am greatly reassured that a lot has changed within the force since this inspection in January 2022."