Changing referenced primary key column type

8.x Db contains tables

create table ametikoh ( ametikoht numeric(7) NOT NULL DEFAULT
nextval('firma1.ametikoh_ametikoht_seq'::regclass) primary key );
create table iandmed ( ametikoht numeric(7) references ametikoh);

I created conversion script which normalizes column types:

alter table ametikoh alter column ametikoht type integer;
alter table iandmed alter column ametikoht type integer;

Running this script causes error:

ERROR: foreign key constraint "iandmed_ametikoht_fkey" cannot be
implemented
DETAIL: Key columns "ametikoht" and "ametikoht" are of incompatible types:
numeric and integer.

How to create script which performs this change and works in 8.0+ ?

Andrus.