Top-down User Stories

Hi All,

My company is developing the strategy for going Agile. Here is how we plan
to maintain the Backlog:

   - product management should specify a "theme",
   - product owner should write User Stories for it,
   - developers should estimate them and eventually split them into tasks.

This strategy is believed to give us a framework to stay on track and to
deliver what product management wants.

Did anybody apply a similar top-down approach in practice?

I like this strategy, but I have a nagging suspicion that this is not an
Agile methodology. Shouldn't the User Stories be created in a bottom-up
fashion in Agile?

I would appreciate your comments. Thanks,

Jana