optimizing large query with IN (...)

Guys,

I got a Java program to tune. It connects to a 7.4.1 postgresql server
running Linux using JDBC.

The program needs to update a counter on a somewhat large number of
rows, about 1200 on a ~130k rows table. The query is something like
the following:

UPDATE table SET table.par = table.par + 1
WHERE table.key IN ('value1', 'value2', ... , 'value1200' )

This query runs on a  transaction (by issuing  a call to
setAutoCommit(false)) and a commit() right after the query
is sent to the backend.

The process of committing and updating the values is painfully slow
(no surprises here). Any ideas?

Thanks.