Is a three years bachelors degree in Commerce and three years bachelors degree in Law from India termed to be equivalent to have a four years graduate degree from the US?
US does not have centralized rules about such things. It's in the hand of each university how they want to handle it.
Very few US universities will admit students with a 3 year bachelors from India. You can check that by writing a mail to the admissions office of the respective university.
Majority of the universities however will not accept the 3 year bachelors. For these universities, you will have to complete 16 years of formal education(10+2+4). This means that you will either have to complete a masters degree or some additional one year degree.
Note that most of the B-schools accept Indian 3 year bachelors nevertheless.
Many universities in the US will not admit students from India (or other commonwealth countries) with 3 year bachelors degrees into graduate programs. In such cases the expectation is that students will have either completed an honors year or gotten a master's degree before applying to the graduate program in the US. In this sense, a 3 year bachelors degree from India is often not considered to be equivalent to a four year bachelors degree.
IISc, IITs etc have BSc/ MSc (Only very few Indian university can offer BS/ MS after proofing that their name will not create any contradiction, like ISI is offering MS(QE), MS(QMS) and MS(LIS), BS/ MS is reserve for Bachelor/ Master of Surgery) degrees equivalent to BTech/ BS/ MTech/ MS, Which are four year Degrees, In addition IITs also conduct MSc programme through JAM, Which are equivalent to traditional MSc degrees. Most of the tier one US Uni doesn't consider 3 year degrees for postgraduate admission in general circumstances (I know some guys who made their appearance in PhD program of Stanford/ Pennsylvania/ Harvard with 3 years degree from ISI) but more than 80% of Uni do accept 3years degree, provided that student has studied in a college having A++ NAAC Grade(3.5+ cgpa) and scored more than 60% or 6.5/7.5 cgpa on 10/9 scale.