I have two very small stretch marks under my chin. Should I get laser treatment to lessen appearance before neck lift?

Laser doesn't work very well on stretch marks and can be risky to do on the neck.  Lasering the neck can result in scarring, which is why many surgeons kaiser the face, but not the neck below the jawline.

I think there is definite advantage to waiting until AFTER your neck lift to treat your stretch marks for two reasons:1. Because the blood flow will be increased as part of healing your stretch marks will turn pink for up to a few months. Many types of lasers will have better results if the treatment is done while they are pink rather than white2. It will give you the opportunity to treat the scar with laser at the same time resulting in faster maturation and turning from pink to white

I would always recommend having surgery before or at the same time as laser. I would caution you against laser first unless you have no intention of having surgery.