Are you looking to restrict certain work types to certain tasks for a particular project? If so this is not currently possible and all of the work types that are associated with a project are available to all tasks for that particular project.
I'm getting confused with estimating time in a task - which can not be allocated to a work type - and estimating time against the project which can only be allocated to a work type.
e.g. How do I create a task, assign to a developer and know that this is time estimated for development (work type)?