trigger speed

I have a trigger that updates a count table, based on status.  The count 
table looks like this:

key  status  count
a        1     300
a        2     400
b        1     100
b        2     200

The problem is that for large updates when I do "UPDATE table SET status 
= 1 WHERE status = 2 and key = 'a';" the row level trigger fires for 
each row updated, decrementing the a 2 row and incrmenting the a 1 row. 
For large updates this really slows things down.

Question #1: how do I speed this up?  I need a way to run a trigger on 
all rows at once.

Q #2: how do satement level triggers work?  The examples in the pg docs 
only show row level triggers.