If your plan allows for in service distributions, you can only do so if you have met a triggering event without incurring a penalty from the IRS for early withdrawals. In order to qualify for an in-service distribution from a 403(b) you must have attained the age of 59 ½ or suffered a disability or have a hardship based on specific financial conditions.
To qualify for a 457 in-service distribution without early withdrawal penalties, you must have attained the age of 70 ½, suffered a disability or have an unforeseen emergency for specific conditions.
If you default on a loan it will be considered a distribution. You will be taxed on the proceeds and may face penalties for early withdrawal.