An "Oilman's Steak Sandwich" is on the menu, calls are being fielded on a remote two-way radio telephone passed from table to table, and independent oilmen are making deals while exchanging greetings with other well-wishers.

The scene is the mint-new, $2.5 million Denver Petroleum Club, filling an acre of space with class and opulence 37 stories above what one oil industry man calls "our little cow town."

The Petroleum Club -- with its recent black tie, grand opening oilmen's ball -- is only the most exquisite example, however, that Denver is no longer a quaint cow town symbolized by the century-old grandeur of the Brown Palace Hotel.

It has become instead the booming oil and mining capital of a desolate but energy-rich Rocky Mountain region now symbolized by the sleek high-rise office buildings called Anaconda, Amoco and Energy Plaza. In ever-increasing numbers, independent oilmen and big oil and mining companies, their suppliers, consultants, lawyers and assorted others are flocking to Denver, and the energy industry has become the most important factor in the city's growth.

So extensive and lucrative has energy become in the region that energy-related loans are now the single biggest loan portfolio at the $1.2 billion United Bank of Denver.

"It's the gold rush syndrome," Frank R. Lee, executive director of the Independent Petroleum Association of Mountain States, says of the "happy accidents that Denver is ideally located geographically to energy deposits and has all the other resources of transportation, communication and banking."

Thus Denver, the only major population and transportation center in the sparsely populated Rocky Mountain region -- it reaches from uranium in New Mexico to coal in Montana -- has become the staging area for the American equivalent of Saudi Arabia's bleak "Empty Quarter"

Here, a geologist makes calculations for a well in Idaho, an engineer plans the mining of coal in Wyoming, a bank provides money for development of an oil field in Montana and lawyers negotiate drilling leases throughout the region. Contract drillers and equipment salesmen work the card and pool tables at the Petroleum Club for projects hundreds of miles away.

"This is the staging point for everything" in the U.S. Empty Quarter," says A.B. (Pete) Slaybaugh, vice president and western division manager for Conoco Oil here. "Very few people recognize the fact you got a [coal] mine in Gillette, Wyo., and it's being run out of Denver. It doesn't connect."

The American Empty Quarter -- the Rocky Mountain region has almost 20 percent of the land but less than 5 percent of the people -- has half of the nation's coal, virtually all of the uranium and absolutely all of its oil shale. It contains the hottest oil and natural gas prospect in the lower 48 states, but until now it has been drilled only half as extensively as Texas.

J. Thomas Reagan, a petroleum engineer who is vice president of the United Bank of Denver, says 413 major energy and mining projects, excluding oil and gas, are planned over the next seven years for the U.S. Empty Quarter, all of them big ticket items like power plants, coal mines and slurry pipelines, rail spurs and exotic coal conversion and geothermal facilities.

"Denver," Reagan says, "is either the headquarters, regional office or district office for all of the companies" planning those projects. He adds that the number of petroleum-related businesses alone in Denver has risen from 858 in 1974 to 1,291 in 1978.

It is estimated that there are now more independent oil companies in Denver than in any other city, including Houston, the city Denver is increasingly compared with. Slaybaugh of Conoco, who has lived in Houston five times during his oil career, compares Denver today to Houston "of the mid-1950s."

The gold rush syndrome began here about 1974, just after the Arab oil embargo forced a new emphasis on the extraction of domestic energy supplies. Since then, says Kathleen Cooper, a corporate economist with the United Banks of Colorado holding company, the value of oil gas and other minerals extracted from the Rocky Mountain region has jumped from $2.6 billion to $5.4 billion in 1977.

And while Colorado's employment grew about 7 percent in 1978, she said, oil gas, coal and mining employment jumped 16 percent.

Denver is not the only Rocky Mountain community to prosper and change as a result of energy development. Reagan reports that 209 communities will be affected by energy projects. In Bell Creek, Mont., for example, his bank financed not only the development of an oil field but the actual community.

The change has been social, political and economic.

Energy companies moving and expanding here have brought highly paid technical and professional employes to pump the area's economy and have filled their gleaming new towers with hundreds of clerical and other support workers. But they have driven up wage scales so that many small businesses are suffering from increased payrolls or an inability to find employes.

Some people see the energy industry restoring a measure of political conservatism that had been lost with the first wave of young, educated professionals that came ot Denve through the 1960s. At the same time, the city has become more cosmopolitan, notes Lee, as he munches lunch in the Petroleum Club: "It used to be there weren't any good restaurants in Denver."

The club is generally regarded as a classy improvement ove its previous "tacky" quarters in the Petroleum Club building. The club managed to grow from 25 members in 1948 to 1,830 today. Lee's organization of independent oil companies has charted an increase in its membership from 300 to more than 1,000 in less than four years.

Despite this prosperity of the energy boom, Denver is racked like a northeastern city by persisting problems. It is losing population while its suburbs sprawl. "The area itself is booming," says an analyst, "but the city has big-city problems."

The Denver city population dropped 35,000 to 479,513 between 1970 and 1976, according to the U.S. Census Bureau, while the entire metropolitan region grew from the nation's 27th largest (1,239,545 people in 1970) to 22nd (1,422,500 in 1976).

Air pollution is legendary. The city enjoyed its first day of good quality air in 18 months when a freak of anture temporarily blew away what is affectionately known as The Brown Cloud. Crime is rising. Last month some people moved out of a North Denver neighborhood because they felt threatened by recurring lawlessness.

Too, high unemployment persists among the unskilled Hispanics, American Indians and blacks who comprise one-fourth of the city's population and who are lost in the area's overall unemployment rate of 3 percent.

In Denver, unlike Houston, the community seems to recognize the problems of growth and an impending necessity of solving them. Conoco's Slaybaugh, who is board chairman of the Chamber of Commerce, says of minorities and unemployed: "It's one whale of a problem, and it's the kind of problem you don't want to live with. It can explode on you."

But for now and for the foreseable future, the explosion is in the oil patch, the uranium mine and coal field -- many of them hundreds of miles from Denver but nevertheless bringing money to this area.

And there is an exuberant certainty here that no matter which way federal energy policy goes in the future it will almost assuredly benefit Denver. For even if the emphasis goes to solar there is an awful lot of sunshine in the Rocky Mountain region, and research is already underway here to use it.