Dear Venkat, there are colleges that offer Undergraduatr courses in Environmental Science. They offer B.Sc in Environmental Science. This course combines Biology, Ecology, Geography, Chemistry, Technology and Social Sciences. To be eligible for this course you should have completed your 10+2 with a minimum aggregate of 50% in Science stream. Few colleges conduct entrance exam while few colleges conduct admissions based on the merit scored in your 10+2. Later you can pursue Masters in any of these subjects and move on to pursue your Ph.D or MS Research. Alternatively, if this course is not available in the States of your choice you can pursue ypur Bachelors degree in any of these mentioned subjects and then move on to do Masters in a specific subject.