I agree with the previous answer. You cannot enter the U.S. in a new status, like an H-1B, without first having a petition approved by U.S. Citizenship and Immigration Services. If you travel to India now, it sounds like you only have an approved L-1B status; therefore, you would only be able to apply for an L-1 visa at the U.S. Embassy or Consulate in India. I recommend that you contact an immigration attorney to discuss your options for changing to another nonimmigrant status, like H-1B, or adjusting to U.S. permanent residence through your employment.
This answer is meant to provide general information and does not create an attorney/client relationship.
If you come back on L-1B, you will need a visa. Likewise a H-1B employer can petition for you. If approved, you will get a H-1B visa and then travel. GC can be sponsored, but the process takes long. So you enter on a non immigrant visa, namely H-1B, and wait until you can adjust status to that of a permanent resident.
This response is general in nature and cannot be construed as legal advice, given that not enough facts are known. Any comments offered on Avvo are of a general nature only, and are not meant to create an attorney-client relationship. If you would like additional information based on this response, please contact my office at 510 657 7665 or 415 902 0832 to schedule a consultation.