Step 1: Use the binomial expansion formula.
The expansion of \( (2 + 3x)^4 \) is:
\[
(2 + 3x)^4 = \sum_{k=0}^{4} \binom{4}{k} 2^{4-k} (3x)^k
\]
Step 2: Find the middle term.
The middle term occurs when \( k = 2 \). Thus, the middle term is:
\[
\binom{4}{2} 2^{4-2} (3x)^2 = 6 \times 4 \times 9x^2 = 216x^2
\]
Step 3: Conclusion.
The coefficient of the middle term is 216.
Final Answer:
\[
\boxed{216}
\]