On March 3, 1997, at 1030 central standard time, a Piper PA-18-150, N2320P, registered to and operated by the United States Border Patrol under Title 14 CFR Part 91 as a public use aircraft, impacted terrain during an off airport landing near Laredo, Texas. Visual meteorological conditions prevailed for the local flight and a company flight plan was filed. The commercial pilot, sole occupant of the airplane, received minor injuries and the airplane sustained substantial damage. The flight originated from Freer, Texas, at 0900. During a telephone interview, conducted by the investigator-in-charge, and on the Pilot/Operator Report, the pilot reported the following information. The pilot was assisting the United States Border Patrol ground agents in pursuit of an illegal alien. The pilot was visually monitoring the pursuit from an altitude of 500 feet AGL. As the alien entered an open field, the pilot considered and explored the possibility of landing the airplane in front of the fleeing alien, reducing the alien's speed, and permitting the ground agents to secure the alien. Winds were from the south at 15 knots with gusts to 20 knots. The airplane was traveling north at 500 feet AGL when the pilot configured (power idle, airspeed 45 mph, flaps 30 degrees) and initiated a 60 degree bank descending turn to the right for landing to the south. During the descending turn, the airspeed increased to approximately 60 mph and when the pilot leveled the wings the airplane had a rapid closure rate with the ground (1,500 to 2,000 fpm). Upon realizing that the descent rate was too high, the pilot initiated a go-around; however, the airplane "impacted the ground in a level flight attitude." The airplane "hit the ground belly first and skidded to a stop." The airplane rotated to the right during the skidding and came to rest 90 degrees to the approach path. The terrain was root plowed ground that was rough with patches of grass. The operator examined the airplane and reported structural damage to the wings, gear, longerons, and fabric of the airframe. The propeller was damaged and the engine remained attached to the airframe.