Hey Dervish.

You cannot  pursue a law degree from USA directly after Class 12th. In USA the degree is called JD or Juris Doctor (3 years) and for admission in this course you need to first complete a bachelor's degree in any subject. Hence you can compare it to a 3 year Law course in India for which too you need to complete an Undergraduate degree like BA, BCOM etc first. 

Unlike USA India has 5 year integrated law courses that combine an Undergraduate degree with Law like BA LLB, BCOM LLB etc in which admission can be taken directly after class 12th. But you can't do the same in USA. For studying law first you need to complete a bachelor's degree first. Then admissions are done on the basis of LSAT.

Best of luck