Yes, torque control of a motor with an AVR microcontroller is possible. In fact, torque control of a joint is common practice in robotics. This is a good example of a feedback loop.
There are many ways to measure the torque of a motor. An expensive way is to use an off-the-shelf strain gauge based force/torque sensor on the output. A cheaper way is to just us a rotary spring and measure the angle before and after the spring. If you have a brushed or brushless motor that you are controlling yourself, the motor's torque is proportional to the current draw. there are ways to measure this electronically as well.
As for control, you will probably use some variant of PID control.