On Monday afternoon, alone on horseback in the Rio Grande ranchland known as Gupierrez vega, Mark Smith was shot in the back.

Two weeks before, Smith had been in Washington to tell Congress about his job as a cattle inspector, or "tick rider," along the Rio Grande. He brought his saddle, which had a bullet hole in it. He said the bullet, fired Feb. 23, was meant for him. He testified that in 1976, his uncle, also a cattle inspector, had been murdered while on duty.

He and two colleagues, also government cowboys, asked for authorization to carry firearms for their own protection. Then they went back to Texas and resumed their solo patrols of the borderland, roping cattle and checking them for disease-carrying ticks.

"I didn't hear the shot, and I didn't see anybody," he said yesterday from Del Rio Hospital, where his condition was listed as very good. "My horse shied up some, though."

Smith and his fellow river riders--there are about 90 in all, employed as GS-7s by the Department of Agriculture--got a careful hearing when they testified at the Longworth Building. One of them, asked what he would do if injured on patrol (they carry no radio on horseback), said: "Why, just mount up and ride for help."

That's what Mark Smith did Monday.

"At first I didn't even know I was shot," he said. "It felt like somebody punched me hard enough to break my arm. It come close to knocking me off the saddle, but no. I rode a ways back to my pickup, I guess about three miles, and loaded my horse on the trailor. I couldn't raise anyone on the truck radio, so I decided to just drive on in."

Smith doesn't know if he passed out or not. "Well, maybe once, when I first got back to the truck. And then maybe once as I was driving in the truck. There wasn't that much blood." He eventually met a sheriff's deputy who took him to the hospital in a police car.

He says he doesn't know who shot him. "Some smuggler, I suppose." He doesn't know if whoever shot him knows his name. "Maybe so, maybe not." Will he be asking for a transfer? "Nope."

Joseph Roman, chief deputy of the Valverde County Sheriff's Department, is investigating the shooting.

"Monday night we rounded up as many deputies as we could and some U.S. Border Patrol, too, and we went out there to Gupierrez vega, looking," Roman said. "We did locate a guy with a .22 rifle, and we got his name. We'll be talking to him some more. An FBI agent is coming over today, because Mark is a government employe."

Roman said incidents along the border are not uncommon.

"There's just more traffic, now. The old wetback with the Coke bottle of water is pretty much gone. There's traffic in stolen automobiles. There are people all doped up hauling wets and who knows what else. There are cattle smugglers. The area Mark patrols is very active, because the river comes within a half a mile from a road down there."

Smith was to be discharged from Del Rio Hospital yesterday. The doctors have decided to leave the slug in his back. They thought that would cause him less trouble than cutting it out.

He was expecting some recuperation leave, "or whatever they come up with," and he admitted that his wife, Lana, is "pretty upset."

Smith has a son named Justin. He was asked what Justin had to say about his father getting shot in the back in Gupierrez vega.

"He didn't say much," said Smith, whose laconic sense of humor was uninjured in the shooting. "He's only 16 months."