Date variables in psql

Trying the following simple sql file:
\set proc_date 6/30/2004
\echo Date is :proc_date
select * from feeds where date = :proc_date limit 20;

If I start psql with the "-a" option I see the output:
\set proc_date 6/30/2004
\echo Date is :proc_date
Date is 6/30/2004
select * from feeds where date = :proc_date limit 20;

and get no records
If I type the exact same query manually it workds
select * from feeds where date = '6/30/2004' limit 20;

Any ideas of the variable may not be recognized on the select statement?