The critical item of information that you need to find (and usually the most difficult to find) is the town name of the specific RC parish in Lithuania where the U.S. immigrant ancestor was born (and baptized). The typical problem with this search is that, although there are many records of your ancestor that have an entry for "place of birth", the typical entry will refer to a much larger area than what you're looking for. For instance, It could say "Lithuania" or "Russia" or "Kowno" or "Wilno". Such a situation often occurs even where the record was asking for an entry of the specific town or village. There is also a chance occurrence of the reverse situation, where you're not expecting to find the name of the town, but Voila!--there it is. So the best approach is to first search the records that are asking for specifics, and then to expand to other records if you don't find enough there. Remember to also search for the birth places of any known immigrant relatives of the immigrant ancestor; it is often the case that they were born in the same RC parish as the ancestor.