I WAS IN college studying biology in 1969 when I ran across an old man in California who made knives. He had a very interesting lifestyle - I liked it."

Jim Fleming seems to have vindicated his choice of the same lifestyle. At 29, he owns and runs the Yonna Valley Forge in Bonanza, Ore., where he teaches and practices advanced knifemaking and ornamental ironworking. It is, by his guess, one of four or five such schools in the country.

He's been in Washington since November on a great to write "an annotated bibliography of blacksmithing," and expects to report it finished at the New York convention of the Artist-Blacksmith Association later this month.

Meanwhile, he's given periodic courses in blacksmithing at Moffett Black- smith Shop in Frying Pan Farm Park, Herndon. The park is a replica of a circa-1920 farm. tilled with horses, and the Moffett shop is all-original, once owned by retired smith Henry Moffett, now in his 80s. It was trundled here from miles away in 1971.

The dirt-floored shop is dominated by a two-eyed brick forge standing against a central wall. The flue narrows up fromm a broad hearth about 3 feet high, which Fleming keeps covered with "coking coal" - soft coal burned to small, insipid cinders. He has a fire going.

A piece of square stock flies in and out of the forge, and Fleming moves fast while the iron's hot - grasps it with tongs, hammers it, dips the metal in borax flux to help burn out impurities, and thrusts it back in the fire to bake.

Ornamental ironworking is distinguished from farrier work and wheelwrighting by its potential for artistry, of which there is only so much in a horseshoe or a wheel rim. Fleming's doorknobs, poker and trivets are embellished with animal heads, scrolling and other decorative work. He spends 30 hours on some of his Damascus-steel knives, applying up to several hundred alternate layers of steel and wrought iron. The Damascus technique became popular in Medieval times when, Fleming says, it was found the layers of iron gave the knife flexibility while the steel lent it strength enough to pierce a helmet and core a man's head. Today, artisans using Damascus-steel number "only a few people. It's so expensive, running $300 - 700, that you really just do it to do it."

Knives of standard designs are considerably cheaper, from $75 to $200 for "straight carbon" inplements and less for kitchen cutlery.

Fleming's work goes mainly to collectors, galleries and museums, including the American Spirit Gallery in the Watergate, the Carriage House in Alexandria, and outlets in Aspen, Vail and Boulder. He's taken some larger projects on commission, and brings out pictures of one of them - $24,000 worth of ornate iron gates, fencing, stairwells and lantern chandeliers at the Timbers Estate outside Denver. It took Fleming and two colleagues six weeks to build the gate alone.

The last 20 years have seen a renasconce in blacksmithing after decades of decline. There are about 2,000 smiths in the U.S. today, compared with a few hundred in the 1950s, and in recent years the Artist-blacksmith Association's membership has about doubled annually.

"The growth field in blacksmithing is in ornamental work," Fleming says. Even the U.S. government is in the market. Fleming wields a tomahawk.

"I made several of thse for the National Park Service. They're made from gun barrels. See, it's actually a pipe" - an ideal hash pipe, someone notes.

Fleming credits frustrated gun hobyists for much of the increased demand for quality knives. "Laws concerning transportation of guns across state lines are becoming so restrictive that people who were buying guns are now buying knives."

Is it a matter of weapons enthusiasts switching from ine incresingly regulated hobby, another that allows more breathing room?

Economic patterns aside, something else changed in those two decades. Fleming does not look like your textbook blacksmith. He eschews leather aprons and gloves, dressing instead in jeans and a blue work shirt over a striped T-shirt. He's good six feet tall, but by no means leviathan - maybe 170 pounds, counting a great deal of darkblond hair and a roughshorn beard.

"Say, where are those 'arms like iron bands?'" someone interrupts a rendition of "Under the spreading chestnut tree . . ."

"I've got them covered up," says Fleming," because I don't want people clamoring for centerfolds."

A half-hour later the iron, bent double and fused at each end, comes out of the fire for the sixth time. Fleming clamps it in a vise, grasps it with tongs, twist it one full turn. The four strands separate above the point of fusion and form a spiral about an inch wide. Fleming loosens the vise, dunks the metal in cooling basin (a garbage can full of water),and brings out the finished product: an open-twist poker handle. The twist is functional as well as ornamental: It dissipates heat by increasing the surface area of metal exposed to air.

One observer said he'd expected a loud racker when Fleming thrust that poker handle in the water. That happens only when large pieces of metal are cooled abruptly, but Fleming began poking in the fire to find a hot piece of a siag that would make a satisfying noise. His tongs came up with what looked like a glossy oatmeal cookie, and he carried it to the water basin and dropped it in.

It shooshed quietly for a half-minute, like a toilet flushing in an area of low water pressure, with a full-bodied, grandually fading sibilance.

"Last weekend we've named these 'cushes,' because of that sound," Fleming said. He indicated a piece of dross about the size of a telephone leaning against the wall, with "Tom's Clinker' scrawled above it in chalk. "That's the champion of the weekend. It hissed a good 10 seconds" (not counting the diminuendo).

Nol Putnam was a 39-year-old school teacher when a book on ornamental blacksmithing impelled him to take the advice he gave his students.

Four self-taught years later, he's "builder, owner, proprietor, chief forger and floor-sweeper" of White Oak Forge, R. R. I, Box 109A, Madison, Va. 22727 (phone 703-948-9252). His back orders ("Right now I'm taking commissions for July") include one for his largest job yet, for hardware restorations at a circa-1820) house near Charlottesville. His work, influenced by contemporary German design, is exhibited at the Tile Gallery on Capito Hill and was included in last year's Decorator Showhouse in McLean.

Putnam's fireplace implements range from $20 - 50 for pokers, average $120 for screens, and start at $90 for andirons. Putnam evolves designs in consultation with customers, submitting "first a rough sketch for a preliminary go-ahead, then proceeding to full-scale working drawings . . . it's all original."