Joining the overheated housing market here in the Mile High City would be relatively easy for anyone making the ownership switch from the Nations Capital. But it's getting a lot tougher for Denverites, who saw both new and resale house prices jump 17 percent during 1977.

And the upswing has continued this year, with existing houses often being resold within three days of being placed on the market. Anything under $65,000 goes fast in this sprawling urban area whose growth has been fueled tremendously by the energy bonanza. Oil and gas exploration and coal and uranium reserves are the cited reasons.

With employment spurting 34 per cent since 1970 and the metro population jumping 26 per cent to 1.6 million in the same period, Denver is in the midst of a new home building boom - 23,000 units annually. As a result of buyer demand, the average price now is $55,000 for a new house and $50,000 for an existing dwelling.

Those prices would not frighten Washingtonian home buyers. But the prices have gone so high so fast in Denver, where a household income of $20,000 is considered above average, that a postal employee and policeman tell you that they'd never make it into ownership in today's market.

Three police officers taking a coffee break near Denver's still-growing, always noisy Stapelton Airport smiled when they admitted to being homeowners. They agreed that it would be difficult to buy now. One said: "I paid $20,000 for a house on 10 acres a far piece out of town. That was ten years ago. Now I hear it would bring $60,000, or more. But where would we go. Besides, we like it there."

Reuben Duran, under 30 and father of one, paid $30,000 for a modest three-bedroom, no-basement house in the fast-growing area called Aurora on the east side of Denver. That was three years ago and Duran, a postal employee, had a VA loan to do it. "We can handle the $277 a month payment and the electric bill for heating isn't too tough ($75 a month in peak heating season). But these new houses nearby are all $40,000 and more now. Sometimes we think about selling this place and moving to the mountains."

While Duran and others talk about moving to the mountains whose snow-capped peaks are visible on good days from most parts of Denver, Marjorie Barrett doesn't plan to give up her small, old intown house that she bought for $13,750 in 1968. "I spent about $10,000 on it and it would go for $72,000 now," said the home section editor and arts writer for the morning Rocky Mountain News.

While new home builders are erecting large subdivisions on relatively treeless tracts to the East and South of Denver (as well as in other areas), the resale brokers are also doing business at a pace that few would have dreamed possible four years ago when the market was markedly depressed. There are fewer houses than usual on the resale market now but the dollar volume vaulted 36 percent in one year.

Resale houses tend to run the gamut familiar to most Americans. New, moderately priced Denver area houses are not unlike the two-story houses one finds in Washington. But Denver knows our split-levels as tri-levels and there are many fewer town houses and apartment condominium units being offered.

Downtown Denver is attractive, a generally uncluttered mix of historic older buildings (including the famed Brown Palace Hotel and the stark remnant of the landmark D & F Tower (now vacant but where apartments for the elderly may be built) and a clutch of Houston-like new towers rising over 30 stories. Preservation and rehabilitation efforts are also under way, as architects do imaginative recastings of old storefront and warehousing areas near the once-bustling railroad station that now handles only a couple of cross-country passenger trains daily.

But while Denver revels in its energy and housing booms, veterans of the housing market are edgy that the dwelling-buying mania could peter out.

"I can't say anything bad about today's total market," said sales director Murray Turner of Perl-Mack Companies.

"The rental market is good, with less than 2 percent vacancy. Yet you can still rent a one-bedroom apartment for $250 a month. But we cannot build for the low end of market today. CAPTION: Picture 1, Examples of Denver's home building market, where a new house averages $55,000:; Picture 2, in the $100,000 range at Shenandoah; Picture 3; a $150,000 model at Gatehouse; a $60,000 Westridge.; Picture 4, Downtown Denver is studded with skyscrapers and rehabilitated buildings. Towers over 30 stories are planned. UPI