TFS Work Items can only be Destroyed, it does not support recoverable deletion of work items.
In TFS 2008 "destroywi" command is used to delete the workitems, which is available as part of TFS 2008 powertools. Whereas in TFS2010, the "destroywi" command has been moved from the Power Tools into the actual TFS administration executable(Witadmin.exe) which will be available at (C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE)
Syntax: witadmin destroywi /collection:collectionurl /id:id [/noprompt]
Usage: witadmin destroywi /Collection:http:\\TestTFSServer:8080\tfs\DefaultCollection /id:12
You can add as many Work Item IDs as you want by using [,] for example 12,15,23 etc.
You can also disable the prompt message by using /noprompt.