To find the Miller indices of a plane, we take the reciprocal of the intercepts of the plane on the axes and reduce them to the smallest integers.
Given the intercepts at \( 3a_1, 4a_2, 2a_3 \), the reciprocals are:
To remove the fractions, multiply all values by 12 (the least common multiple):
Thus, the Miller indices of the plane are:
\[ (436) \]
Therefore, the correct answer is (A) (436).