deleting bookmarks=spinning beachball

For many months deleting my Safari bookmarks has been excruciating. I click on the book icon, expand the Bookmark Bar portion (or any portion), highlight a bookmark, click the Delete button or Control>Delete. It deletes one just fine. I immediately try to delete a second one and the spinning beachball comes up for many many seconds. I just timed one and the ball spun for 30 seconds. I tried to clean up bookmarks several months ago and after spending far too long watching the beachball I gave up. I have old bookmarks I would like to remove because my I have too many bookmarks, but it takes so long. What can I do to correct this? I have emptied cache this week (don't know if it affects bookmarks) but haven't touched any plist files.

Thank you!

iMac 2009

4 GB RAM

1 TB storage w/530 GB used

running OS 10.7.5