At work in his office in the wasteland along the railroad tracks in Silver Spring, Perry Van Vleck looks much the way you'd expect a healthy 64-year-old real estate man to look.

But pat him on the should or shake his hand and you know you've locked onto somebody who's tussled with rougher stuff than deeds and closing costs.

He's hard as two-by-fours and proud enough of it slip off his jacket and offer you a friendly poke at his neck muscles - rope steel.

He built those ropes in 25 years of stalking the purest game fish there are - bluefin tuna, black marlin, blue marlin, broad billed swordfish, striped marlin. And Van Vleck spares no expense in guaranteeing the best odds for landing record-breakers.

His plans already are set for this year. In March he'll be in Cozumel, Mexico; he'll hit Cape Hatteras in July; in September he'll be in Venezuela; in October he'll chase giant tuna off Prince Edward Island and he'll journey to Honduras in December.

That's just what's scheduled. Other trips are almost assured. And between times he'll fly fish for bluegill and bass in the pond at his farm in Calvert County and chase blues in the Chesapeake and sea trout in the Delaware Bay.

The one trip Van Vleck makes every year is to the International Tuna Cup competition in Nova Scotia. Last year he didn't fish while he was there because he was too busy working as organizer for the U. S. team. Afterward he took off for two weeks of tuna fishing off Prince Edward Island and had what may be his greatest week. In three days he landed two mammoth bluefins, one an even 1,000 pounds and the other 927.

Van Vleck is rigged to fight. He uses 130-pound test line on a Fin-Nor 12/0 reel and a heavy duty Shakespeare rod. The reel alone cost $1,250, he said, and Van Vleck keeps two lest one should break.

His favorite sport fish is tuna. "It's the toughest fish in the ocean, the king of all the big-game fish. Many fish are bigger, but tuna fight as hard as any. They are consistenly harder to catch than any fish."

Van Vleck has the credentials to make those assertions. There's a picture of him in S. Kip Farrington's book on the Nova Scotia competition, "The Sharp Cup," that shows him standing beside the carcass of a 784-pounder he fought for 5 1/2 hours before boating in the 1971 match.

Hisgrin's as wide as the tail fin.