For applicants to law school for Fall 2007, the average "Caucasian/White" applicant to law school had an LSAT score of 154.9, and an undergraduate GPA of 3.32. The average "Black/African American" applicant had a LSAT score of 143.7 and an undergraduate GPA of 2.96. The standard deviation for LSAT scores is 9.97.
For law school matriculants in Fall 2007, the averages were 158/3.40 for whites, and 150/3.16 for African Americans.
Asian Americans had very similar scores to whites, on average, and Hispanics' scores were very close to midpoint between the scores of whites/Asians and African Americans.
This is, of course, not the whole story. A large percentage of matriculants (admitted law students) have below average LSAT scores and GPAs. Most law schools consider historical data on grade inflation at your undergraduate institution, which the law school data assembly service conveniently makes available to them. Grade trends, essays, recommendations, legacy considerations, race, geography, undergraduate major and other elements of your personal story can also make a significant difference at the margins. No particular undergraduate major is required and there are no courses that a pre-requisite to law school attendance.
But, if your grades and LSATs are at or near the average for matriculated law students, you have a very good chance of being admitted to law school somewhere, if you apply to schools with a range of selectivity (i.e. if you apply to a safety school or two appropriate to your grades and test scores). On the other hand, if your grades and LSATs are well below the average for matriculated law students, you need to carefully study the details of admissions practices at various law schools and apply to as many schools where you have some chance of being admitted as possible, if this gives you a real chance of being admitted.
The empirical evidence suggests that one needs roughly a 2.8 undergraduate GPA and 149 LSAT score (a score which is at roughly the 40th percentile for LSAT test takers) to have a realistic chance of passing the bar exam. A certain amount of tradeoff between grades and LSAT scores is possible, if high grades do not simply represent grade inflation at your undergraduate institution relative to other colleges and universities.
If your grades and test scores are not at that level, you should seriously consider some endeavor other than law school, which is very expensive, does not have widely available grant aid, and is a poor use of your time if you don't end up getting admitted to the bar.