The formula for the point \( P \) on a line segment joining two points \( (x_1, y_1, z_1) \) and \( (x_2, y_2, z_2) \) is given by:
\[
P = \left( \frac{x_1 + x_2}{2}, \frac{y_1 + y_2}{2}, \frac{z_1 + z_2}{2} \right)
\]
Here, we are given the points \( (3, 2, -1) \) and \( (6, 2, -1) \).
Using the formula, the coordinates of \( P \) are:
\[
P = \left( \frac{3 + 6}{2}, \frac{2 + 2}{2}, \frac{-1 + (-1)}{2} \right)
\]
Simplifying:
\[
P = \left( \frac{9}{2}, \frac{4}{2}, \frac{-2}{2} \right)
\]
\[
P = \left( 4.5, 2, -1 \right)
\]
Thus, the point \( P \) divides the line segment in the ratio 1:1 and is located at the point \( (4.5, 2, -1) \).
Therefore, the correct value of \( P \) is \( \boxed{2} \).