Years ago, when the Dallas Petroleum Club was down Commerce Street in the old Adolphus Hotel, life was a lot less formal. "Why, my father used to come to lunch at the old club in a sports shirt," recalls Clinton William Murchison Jr., the megamillionaire venture capitalist whose varied holdings include the Dallas Cowboys." And he'd wear sandals - no socks. Maybe that was because he had athletes' foot."

Clint Murchison, 54, takes a long drink from his fourth glass of wine and shoots an owlish glance across the table. The tag line about his father's podiatric problems may have been one of those Texas-dry jokes for which Murchison is a legend among his cronies. Murchison has been known to spend weeks, even months, planning a practical joke - like the time he put the walkie-talkie into a friend's golf bag which crackled out a choice remark at the very moment the friend was trying to make a crucial shot.

During a 3-hour lunch recently at the splendid setting of the current Dallas Petroleum Club. Clint Murchison, whose wealth dwarfs even the fabulous fortune left by his oilman father, Clint Sr., ranged over numerous subjects from his father's feet to his favorite football team to his most promising investments to the family fortune and to his political views.

Though a member of Murchison's tight circle of friends said that "he is generous with everything but his time," Murchison agreed to the rare interview after it was noted that his millions are having an increasing impact on the Washington economic, political and social scene.

Murchison established a franchise for the Dallas Cowboys professional football team in 1960 over the violent objections of George Preston Marshall, then the owner of the Washington Redskins club. As tomorrow night's contest approaches, it is clear that the passage of nearly two decades has only intensified the rivalry between the two National Football League teams.

In June, it was announced that Murchison company had contracted a 99-year lease on the largest piece of private property in the District of Columbia, the 40-acre John Archbold estate on Reservoir Road NW. Plans call for Murchison to erect 300 detached and clustered houses, each of which will sell for $300,000 or more.

And in Rockville, Murchison-controlled Optimum Systems Inc., a computer company he created 10 years ago to analyze the performances of would-be Dallas Cowboys from high school through college has diversified to become a major force in the health-care-billing business.

Murchison is well aware of the impact of politics on his fortune, so for 27 years he has retained Thomas Webb, a former FBI agent, lawyer, former University of Maryland football player and well-known native son of Washington. Each year for as long as anyone can remember, Webb has hosted - and Murchison has financed - the "bull and bear night," a stictly stag gathering of 300 or more representatives of big business and politics at Webb's Potomac estate. Participants compare golf scores and eat wild boar, venison, buffalo and the like. Honored guests have included the late Sen. Hubert Humphrey (D-Wisc.) and former Attorney General Richard Kleindienst.

A favorite question about Murchison, of course, is just how rich is he. Murchison himself apparently doesn't have a figure. When asked, for example, for the annual sales of Optimum Systems, Murchison says, "Oh, about $30 or $40 million. I really don't know."

No less authoritative source than Town & Country magazine, that chronicler of the very rich, recently rated Clint and his brother, John Debney Murchison, 56, as among "the wealthiest Americans." T&C put the Murchison boys in the $200 to $300 million category, but other equally informed sources peg their wealth at twice that.

The fountainhead of the Murchison millions was Clint Sr., one of the giants in the colorful history of oil. In his book, "The Reluctant Empire," George Fuerman says of Clint Murchison, H.R. Cullen and H.R. Hunt: "The three men, with little help from others, have made Texas oil, and thus Texas, a national antipathy."

Born the son of a Athens, Tex., banker Clint Sr. was too restless to spend his life in a cage. He teamed up with his boyhood buddy. Sid Richardson, and together they discovered enough oil to earn them the moniker "the New Athenians." With all the money in the world, the two men began dobbling in politics and both men gave their generous backing to boost Lyndon Johnson into theSenate. More recently, it was the foes he collected as executor of Richardson's estate that made a millionaire out of another political friend of the oilman, John Connally.

Clint Sr. sent his sons to exclusive Eastern prep schools. John went on to Yale, Clint to M.I.T., where he got a masters degree in math. While still in their 20s, the brothers were given a sizable chunk of their father's fortune to manage. According to one report, they used the money to buy into or establish about 100 companies, and before long they had doubled the stake to about $150 million.

But it was in 1961 that the Murchison brothers took on the Wall Street establishment when they unsuccessfully challenged the 68-year-old Woolworth heir, Allan P. Kirby, for control of the vast holding company, Allegheny Corp. Its rich holdings included control of the old New York, Central Railroad and the giant Minneapolis investment firm, Investors Diversified Services, which had assets at that time of $3.4 billion.

The celebrated battle put the Murchison boys on the cover of Time magazinesome seven years after their father made it for being a super-rich Texan. In the years since, what little publicity the Murchisons have gotten has been a result not of their business dealings but of their dealings with political figures.

The Murchisons run their diverse empire from a floor of office space a few stories down from the Dallas Petroleum Club. Clint jokes about his brother's extraordinary collection of modern objets d'art that line the walls and fill the corners of the office. Clint is more comfortable in his own surprisingly small and cluttered corner office. Judging from the books carelessly stacked atop most surfaces, Murchison taste in reading matter is strictly practical: subjects like inheritance taxes and investment tactics. And his collecting is limited to ashtrays and doll figures emblazoned with big "D"s for the Dallas Cowboys.

The Cowboys are more than just another business investment to Clint Murchison. He loves the game of football in general, and his Cowboys in particular. Even so, his approach to this passion is, as usual, business-like. Murchison is customarily vague about the earnings of the Cowboys. "It's not a money-making business," he says. "Everytime we get a new TV contract - we've had three in the past 10 years - the extra money goes into salary increases for the players."

The Green Bay Packers are the only publicly owned team, and therefor the only one that publishes its balance sheet. According to Murchison, the Cowboys make less than Green Bay, which last year had net income of $266,810 on revenues of $7.1 million. A spokesman for Green Bay called Murchison's claim "a bunch of nonsense."

He claimed that that the Cowboys are among the lowest-paying teams in the league, pointing out that, at his peak, Dwayne Thomas was earning only $20,000 a year. "Hell, they make a fortune just selling posters of those Cowgirls. They've sold 500,000 of those already at $2 a crack," the Green Bay spokesman claimed.

In 1969, not long after organizing the Cowboys, Murchison found that his managers were accumulating vast amounts of research on each candidate for a Cowboy slot: When he went to IBM to get a computer to handle it all, "We were told that we had more variables than the existing systems could handle," Murchison recalled.

So he get a professor at California Polytechnical Institute to design a system, which Marchison says cost about $1 million. What he got for his money was a system to advanced that NASA used it for the first moon flight.

To help defray the expense of the computer, the Cowboys set up a joint venture with the Los Angeles Rams and the San Francisco Forty-niners. But Murchison had more ambitious plans for the system.He set up Optimum Systems to handle the billing for various state federal and private medical plans.

But he quickly realized that the field was dominated by a company run by Dallas neighbor H. Ross Perot. Many states and insurance carriers had computer systems designed to mesh with the system at Perot's Electronic Data Systems Corp., says Murchison. "Four or five years ago in California, we were low bidders by $4.5 million on a $20 million contract, and Perot got it," he says.

Smaller computer companies have not been able to stand up to EDS, which had revenues of about $135 million last year. But Murchison had the resources to buck Perot. "Maybe it was cause I got mad and felt I was being put upon," he says, adding that Optimunt Systems, of which he owns 90 percent, has "turned the corner" and is making a profit.

Clint Sr. quickly diversified out of oil and gas, leaving about one-fifth of his investment dollars in that business. His sons have followed suit. The Murchisons' Delhi International has oil and gas leases in Australia and elsewhere. They also have coal properties in New Mexico, Kentucky and West Virginia.

Kirby Exploration runs a chemical barge line. They own "six or seven" Texas banks.