NFL Star Justin Blackmon -- ARRESTED FOR WEED ... Two Blunts

Troubled NFL wide receiver Justin Blackmon was arrested in Oklahoma on Wednesday -- after cops say he was driving around with TWO BLUNTS in his car ... this according to police.

TMZ Sports obtained the police report filed by the Edmond Police Department which says Blackmon was driving a 2007 Chrysler 300 sedan when he crossed into oncoming traffic to get around stopped cars.

During the traffic stop, the arresting officer says he smelled weed -- so he asked Blackmon to get out of the car and HANDCUFFED him so they could search the vehicle.

The cop noted, "I noticed that he was rather large in stature and appeared to be physically fit."

According to the report, 24-year-old Blackmon admitted to having 2 blunts in the car -- one smoked, one fresh. Cops searched the car and found the blunts ... the fresh one neatly packed in a Swisher Sweets box.

The #5 overall pick in the 2012 NFL Draft was then arrested and transported to a nearby jail -- where he was cited for possession of weed and "improper passing on the left."

The cop notes Blackmon was "extremely honest and cooperative" throughout the incident.