In downtown Denver three new office buildings are under construction. 10 others have been built in the last four years and six more are due to go up by 1980. For this city is in the throes of an energy boom that is making it another Houston. So a close look at what is happening here says a good deal about what Washington should be doing - and not doing - in developing a national energy policy.

Six states and four fuels are involved in the sudden upsurge of business in the Mile High City. There are huge deposits of relatively sulphur-free coal in Colorado, New Mexico, Wyoming and South Dakota. Uranium is plentiful in New Mexico, Wyoming and Colorado, Oil and gas abound in Nebraska, Utah, Wyoming and Colorado.

Denver is geographically at the hub of all the action. Besides being a transport and financial center, it is an extremely pleasant place to live - ranked fourth in the country (after Seattle, Eugene, Ore., and Minneapolis) in a study by Family Circle magazine.

So the energy corporations have been moving in headquarters or expanding existing offices. The number of oil and gas companies in town has grown from 350 to over 1,000 in the past four years. A dozen coal and uranium companies (including Anaconda) have moved their head offices here since the Arab oil embargo of 1973 began sending energy prices sky high.

The work force, which has grown by 35 per cent since 1965, is due to go up another 33 per cent by 1985. In the past year alone more than 3,000 new construction jobs have opened up.

Vacant office space downtown is practically impossible to find. While home-building is limited by various zoning restrictions, one real-estate executive likens that market to "a dog running at the end of a leash."

Perhaps most impressive is Stapleton Airport, which the energy executives use for commuting to the development sites. Stapleton serves the 25th largest city in the country, but ranks eighth in number of commercial flights, and fourth if the private and nonscheduled planes favored by the independent oil companies are included.

Possibly because many small companies, rather than a single giant, were involved, the Denver boom was hard to spot at first. But recently The Denver Post ran a six-part series on the city's growth, and several local businessmen are beginning to talk things up.

One of the most successful, and buoyant, is Marvin Davis, a transplanted New Yorker said to have made over $300 million in oil and gas, real estate and banking. "The future of Denver is untold, unbound and unlimited," Davis says. "Energy-wise, this is the future of the United States."

Also the present. The Denver boom shows thousands of operators are already turning on the tap for a bigger and bigger flow of energy. Every drilling rig in the country is now at work, and shortages are developing in critical skills and machinery.

So clearly incentives are more than adequate. The tax and deregulation issues to furiously discussed in the Washington debate on the energy bill may spell the difference between big and very big profits, but they are not crucial to production.

What does bug virtually everybody here, including one of the country's best known environmentalists, Gov. Richard Lamm, is red tape. Federal, state and local regulations govern land-leasing, use of water and building of access facilities. Months and sometimes years go by before clearance can be obtained for energy products. Even Lamm, who is virtually a nut in his insistence that the environment not be disturbed and that plentiful water be left for farming, acknowledges the critical importance of "expediting procedures."

Marvin Davis claims that he has discovered in Wyoming a gas field with three-quarters of a trillion cubic feet. All he needs to bring out the gas is construction of a 14-mile pipeline, which he estimates would take 30 days. But he has waited 15 months to get authorization for the pipeline from the Federal Power Commission and expects to wait another 6 to 10 weeks.

He fears he will then have to spend a year or so getting an acceptable environmental-impact statement from the Interior Department, which might then be contested by the Environmental Protection Agency. "Meanwhile," he laughs, "they're freezing back East."