It's probably safe, but I wouldn't do it. In my opinion, lagers are much more delicately flavored, and "cleaner", and I get it off of the primary yeast cake right after the diacetyl rest. I don't think keeping the beer on a yeast cake for 3-4 months is good practice although it may not ruin the beer.
I primary at 50 degrees for about 10 days, then do a diacetyl rest for 48 hours at 60 degrees (assuming the beer is about finished in the primary- you'd have to check the SG). Then, I rack after the diacetly rest and get ready for lagering. I lager for one week for each 8-10 points of OG, so for a 1.064 lager, I'll lager about 8 weeks. I like to lager at 34 degrees, as I find that it gives the smoothest flavor.