That depends entirely on what yo consider "extremely powerful". I think you're way overestimating what it takes to get an object to be moved aside.
Okay, I can do some math. It's not my favorite pasttime, but I've kind of gotten myself curious about this anyway.
There's a 1 gram object moving at C/10 meters per second directly towards the center of a starship. We'll use the ship's frame of reference here so that we can consider it stationary.
Let's say the object needs to be moved x distance to the side to avoid a collision, and it is first acted on at distance y. x and y are in meters.
For simplicity, let's say the force applied by the deflector is directed in the desired direction of movement (to the side). There may be some benefit to directing the force slightly away from the ship to slow down the object, but that complicates the equation and I
suspect won't change the result much.
Since the force is entirely to the side, the deflector has only 10*y/C seconds to move the object to the side before impact. Assuming the force applied is constant, velocity to the side will increase linearly from zero; and we require that the integral of the velocity from times 0 to 10*y/c is equal to x. As this is a triangle, this gives us that x = 5*y*v/C if v is the final velocity at impact (or not) time. We can rearrange this to be v = x*C/(5y).
So we can take the derivative of this velocity to find the necessary acceleration: v/t = a = (x*C/(5y))/(10*y/C) = x*C*C/(50*y*y). We can sanity-check that the units here are m/s^2, which indeed they are.
Now that we have the acceleration we can find the force. Newtons have the units kg*m/s^2, so the force required to deflect the object would be F = x*C*C/(50000*y*y) Newtons.
To give a few examples, if the effect of the navigational deflector extended 5000 meters from the ship and the size of the ship was 1000 meters, then we would have F = 71,900,414.3 Newtons.
72 Meganewtons for a 1-gram bullet. If it's 2 grams, that doubles. That's a lot of force. Maybe not outside the realm of possibility, but nothing to sneeze at either. If the nav deflector can do that, I don't dare speculate on the tractor beam's capabilities!
Also, the deflector dish is pointed ahead of the ship. Together with the fact that the fastest (relative) impacts would be approaching from the front during normal operations, it's a safe bet that the deflector envelope isn't spherical. That could render the ship more vulnerable from particular directions if the deflector field doesn't extend as far that way.