I think this will help you - Message from Ambassador Robert D. Blackwill
Two changes to INS visa regulations may affect Indians seeking US visas. One change has already occurred, and approval of the other is pending. The INS has implemented a procedure that will limit student visa adjustments within the US, but will not affect legitimate student visa applicants applying abroad. In the past, foreign students could visit the US on a tourist visa and, while in the United States, could apply to change from a tourist (B-2) to a student visa (F-1). This is no longer allowed.Indians
wishing to study in America should have their student visas issued in their country of residence before they go to the United States. This will not affect a person\'s ability to study at his or her chosen university. In its continuing effort to enhance national security and strengthen immigration controls in the United States, the INS has proposed modifying the current admission period for B-1/B-2 non-immigrant visitors. In the past, the INS allowed most visitors a six-month stay in the US, regardless of the time they required. Now, the INS proposes to base the admission period on the amount of time the visitor requests in order to accomplish the purpose of his or her trip. This modification has been wrongly described as allowing visitors "only" a thirty-day visit to the US. That is not accurate. If this change of rule is accepted, the INS inspector at the port of entry in the United States would ask all visitors how much time they require to complete their visit. If a visitor does not request more than thirty days in the US, then he or she would generally be granted a stay of 30 days. If the visitor needs more than thirty days, the longer period would normally be approved.