The earth is slightly closer to the sun in dec. than it is in june.  the force of gravity of the sun on the earth in dec. compared to june is slightly

Slightly greater gravitational force.

Gravity follows the inverse square law, specifically in Newtonian physics we can use the following equation:

Let's focus on the part of the equation which denotes the distance between these two objects.  So if the distance is smaller, we will get a larger gravitational force, and if the distance is larger we will get a smaller gravitational force.  Therefore, since in December, Earth is slightly closer to the Sun then we would experience a slightly greater gravitational force.