altering table with default value

Hi, How to alter a table with default value?
I am using the below statement, But, it is not working..Any pointers?
Thx..
----------
alter table action_item ALTER COLUMN STATUS default 0ALTER TABLE ACTION_ITEM ADD CONSTRAINT
DF_ACTION_ITEM_STATUS DEFAULT 0 FOR STATUS
GO
UPDATE ACTION_ITEM SET STATUS =0 where STATUS IS NULL
GO