John Paul spoke against it, but most other leaders disagree. American bishops are in favor of it and against it, depending on who asks and who is asked. There's information all over the Web, if one can get past the public relations junk.
Concern That US Bishops' Conference Folding On Federal Marriage Amendment
http://www.lifesite.net/ldn/2004/may/04051407.html
48 House Catholics send warning to bishops
http://www.msnbc.msn.com/id/5017313/
"American bishops are in favor of it and against it, depending on who asks and who is asked."
With a high proportion of sodomites among the American bishops, their reticence to condemn homosexual unions should come as no surprise.
It would be like a doctor condemning the practice of medicine.