LeGarrette Blount -- Weed Charge Dropped ... Completes Comm. Service Ahead of Schedule

Good news for LeGarrette Blount ... prosecutors have dropped the pot charge against the New England Patriots running back after he completed his community service days before the deadline.

As we previously reported, Blount -- along with Steelers running back LeVeon Bell -- were arrested in Pittsburgh back in August after cops say they had weed inside their car.

Bell was arrested for DUI -- but struck a plea deal in which prosecutors agreed to drop the charge if he completed 15 months probation without incident.

Blount struck a similar deal on his misdemeanor possession charge -- complete 50 hours of community service by Feb. 4th and the charge goes away.

Now, Blount's attorney claims he's done just that -- completing his comm. service at the Urban Achievers group in Boston ... which works with underprivileged children.