How to add "on delete cascade" constraints

Hello,

in 8.4.9 is it please possible to add "on delete cascades" to
the both foreign keys in the following table w/o dropping the table?

# \d pref_scores
Table "public.pref_scores"
Column | Type | Modifiers
---------+-----------------------+-----------
id | character varying(32) |
gid | integer |
money | integer | not null
quit | boolean |
last_ip | inet |
Foreign-key constraints:
"pref_scores_gid_fkey" FOREIGN KEY (gid) REFERENCES pref_games(gid)
"pref_scores_id_fkey" FOREIGN KEY (id) REFERENCES pref_users(id)

There referenced tables are below:

# \d pref_games
Table "public.pref_games"
Column | Type | Modifiers
----------+-----------------------------+----------------------------------------------------------
gid | integer | not null default
nextval('pref_games_gid_seq'::regclass)
rounds | integer | not null
finished | timestamp without time zone | default now()
Indexes:
"pref_games_pkey" PRIMARY KEY, btree (gid)
Referenced by:
TABLE "pref_scores" CONSTRAINT "pref_scores_gid_fkey" FOREIGN KEY
(gid) REFERENCES pref_games(gid)

\d pref_users
Table "public.pref_users"
Column | Type | Modifiers
------------+-----------------------------+---------------
id | character varying(32) | not null
first_name | character varying(64) |
last_name | character varying(64) |
female | boolean |
avatar | character varying(128) |
city | character varying(64) |
login | timestamp without time zone | default now()
last_ip | inet |
logout | timestamp without time zone |
vip | timestamp without time zone |
mail | character varying(254) |
Indexes:
"pref_users_pkey" PRIMARY KEY, btree (id)
Referenced by:
TABLE "pref_cards" CONSTRAINT "pref_cards_id_fkey" FOREIGN KEY
(id) REFERENCES pref_users(id)
TABLE "pref_catch" CONSTRAINT "pref_catch_id_fkey" FOREIGN KEY
(id) REFERENCES pref_users(id)
TABLE "pref_chat" CONSTRAINT "pref_chat_id_fkey" FOREIGN KEY (id)
REFERENCES pref_users(id)
TABLE "pref_game" CONSTRAINT "pref_game_id_fkey" FOREIGN KEY (id)
REFERENCES pref_users(id)
TABLE "pref_hand" CONSTRAINT "pref_hand_id_fkey" FOREIGN KEY (id)
REFERENCES pref_users(id)
TABLE "pref_luck" CONSTRAINT "pref_luck_id_fkey" FOREIGN KEY (id)
REFERENCES pref_users(id)
TABLE "pref_match" CONSTRAINT "pref_match_id_fkey" FOREIGN KEY
(id) REFERENCES pref_users(id)
TABLE "pref_misere" CONSTRAINT "pref_misere_id_fkey" FOREIGN KEY
(id) REFERENCES pref_users(id)
TABLE "pref_money" CONSTRAINT "pref_money_id_fkey" FOREIGN KEY
(id) REFERENCES pref_users(id)
TABLE "pref_pass" CONSTRAINT "pref_pass_id_fkey" FOREIGN KEY (id)
REFERENCES pref_users(id)
TABLE "pref_payment" CONSTRAINT "pref_payment_id_fkey" FOREIGN KEY
(id) REFERENCES pref_users(id)
TABLE "pref_rep" CONSTRAINT "pref_rep_author_fkey" FOREIGN KEY
(author) REFERENCES pref_users(id)
TABLE "pref_rep" CONSTRAINT "pref_rep_id_fkey" FOREIGN KEY (id)
REFERENCES pref_users(id)
TABLE "pref_scores" CONSTRAINT "pref_scores_id_fkey" FOREIGN KEY
(id) REFERENCES pref_users(id)
TABLE "pref_status" CONSTRAINT "pref_status_id_fkey" FOREIGN KEY
(id) REFERENCES pref_users(id)

Regards
Alex