the verb form is 사랑하다
but when you use it, you will not say "사랑하다". You will say "사랑한다"
You will say:
"사랑합니다" (sarang hamnida) ... superior formal
"사랑해요" (sarang haeyo) ... superior informal
to parents, grandparents, teacher etc.
"사랑해" (sarang hae) ... informal
sometimes ... "사랑한다" (sarang handa)
to your lover, brothers/sisters
the most commonly used form is "사랑해" because people wont say "我愛你" to someone they dont know. Superior form is not common. Also nowaday most Korean children/younger person say in informal form to their parents or the elder ones. Therefore, they will say "사랑해" to parents, grandmom, teacher etc.
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Actually, l'm not quit keen in answering such question as there are lots of answers here. lf you take some time and do a search here, you will find the answer and there is no need to raise this question.
It's just that there are some small errors in pronounciation and the form used that's why l answer this. Sorry everyone.
For example see here for an answer (though not exactly correct in pronounciation):
http://hk.knowledge.yahoo.com/question/?qid=7007021202573