SET AUTOCOMMIT TO OFF

Please, could someone point me to the right list
or tell me how to do a "SET AUTOCOMMIT TO OFF" within libpq.
The case is pretty urgent, as we have to move our applications
to Linux and thought it's better to use PG7.4.
We used to have PG7.3 under HPUX, and we think of a temporary
downgrade back to 7.3 under Linux, if we cannot solve the
SET AUTOCOMMIT TO OFF case.
A simple "No, it's no longer available" or
"Yes, it goes like ..." by someone from the core developers
would be greatly appreciated.

Following what I was asking the other day:

Since the server-side autocommit off was abolished in 7.4
I am looking for a session-wide replacement, meaning
as long as one connection is running, after every COMMIT
the next SQL-command triggers an implicit BEGIN.

The Release Notes on 7.4 state
The server-side autocommit setting was removed and reimplemented in
client applications and languages. Server-side
autocommit was causing too many problems with languages and applications
that wanted to control their own autocommit
behavior, so autocommit was removed from the server and added to
individual client APIs as appropriate.

So basically, I cannot find the autocommit-off-switch within the libpq
interface.

TIA
Regards, Christoph

BTW
In ./postgresql-7.4.5/doc/html/ecpg-commands.html
there is still a line saying
This mode can be explicitly turned off using EXEC SQL SET AUTOCOMMIT TO
OFF.