If there is room in first, you won't be cleared into Y, you'll just be cleared into F. You should go to the top of the UG list (barring any PE's with higher fare classes) and go to the top of the standby list as well.

See NWA012's comments in this thread too.

http://www.flyertalk.com/forum/north...e-process.html

I've had it several times that I do standby, don't have a Y seat, and they will clear me into F. One time I wasn't cleared into F, but I was at the top of the list. They just cleared me into Y at the last minute when F was full.

I've never done standby knowing I couldn't get on though, one of the bennies of plat.