How to set enable_seqscan=off for Postgresql query in php?

[phatcher]

I need to turn off enable_seqscan on a Postgresql query I'm running from my app.
I use this line:
#Turn off enable_seqscan
$result = pg_query($db,"set enable_seqscan=false;");
but I have no idea if it works. I tried to return the value from $result, but there is no data. I also tried using
$notice = pg_last_notice($db);
but no data was returned. This leads me to believe it was not set. Any idea how to set this value?
TIA
Patrick