plpgsql select into question

sorry if I've sent this to the wrong list...

what is the proper way to do the following from within a plpgsql proc:
(where table2 is a variable...)

select into user_id max(id) from table2

This is part of a procedure that inserts a new record into table1 (table1
has an auto-incrementing id field). Then a trigger inserts a new record into
table2 using max() to get the new id from table1 (the trigger fires after
insert on table1), then the procedure updates table2. In order to update
table2, I need to get the max(id) so I can do:
update table2 set .... where id = user_id

Thanks very much. And I'm grateful for ideas about a better strategy.
cheers,
jd

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