A phenomenal commercial construction boom is under way in the United States and has given rise to a new feature on the urban scene -- the "see-through building."

The "see-through building" -- vacant new office buildings with no tenants and, hence, no interior walls -- can now be found from Atlanta to Seattle and from Houston to Indianapolis.

More office space has been built in the last five years than in the decade of the 1970s, figures show. And, at a time when leasing agents consider 5 percent a comfortable vacancy rate, more than 14 percent of the nation's first-quality downtown office space is unoccupied. In the suburbs, the figure is 18 percent, according to one survey.

The District of Columbia's rate was 12.2 percent downtown, although Lewis Bolen of Real Estate Research Corp.'s office here said he believes that the rate is more like 15 percent, if sublet space is included, and 10.6 percent in the suburbs.

In contrast to the boom-and-bust cycle of past years, construction is continuing briskly, all but guaranteeing future years of double-digit vacancy rates in most cities. Developers acknowledge the overbuilding. "There are too many starts all over the world," Washington builder Oliver T. Carr Jr. remarked. But developers press ahead anyway.

The reasons they are willing and able to do so are complex, but most industry observers point to:

*The dramatically improved tax treatment accorded real estate in recent years. Investors now can depreciate their buildings over 15 years -- raised to 18 by Congress last summer -- instead of the former "useful life" of the building, perhaps 40 years. This means that buildings can generate paper losses that can be sold to high-bracket taxpayers.

*Deregulation of lending institutions. Competition for deposits has bid up interest rates on them, putting pressure on institutions to try for better yields on their investments.

*The enormous growth of foreign investment. Sometimes fleeing instability at home, more often just looking for a better return, foreign investors have pumped vast sums into American property. A study by Washington real estate consultant Mahlon Apgar IV puts such investment at $49.5 billion from 1979 through 1983.

*The relatively poor performance of other types of investment. Real estate has generally kept up with inflation, which makes it particularly appealing to investors who fear a resurgence of inflation.

No one of these factors alone accounts for the amount of building that is taking place, but together their effect is explosive. For example, improvements in the tax treatment boosted prices, which in turn helped real estate's performance when compared with, say, stocks.

The results, however, look peculiar when viewed from street level. In cities across the country, construction is continuing while completed buildings stand partly or completely empty. Bargain-hunting tenants negotiate for long periods of free rent and lavish improvements to the space they do take.

Of 31 markets tracked by Coldwell Banker Commercial Real Estate Services, only seven (including two Manhattan submarkets) showed single-digit vacancy rates at the end of the third quarter of 1984, and none was as low as the "comfortable" 5 percent. The closest was midtown Manhattan at 6.6 percent.

Of 30 suburban markets, Coldwell Banker found none with a vacancy rate of less than 10 percent.

Particularly hard hit have been the Sun Belt and energy-producing areas. More than 20 percent of Houston's downtown space was vacant and more than 30 percent of its suburban offices had no tenants, according to Coldwell Banker.

Likewise, Denver's downtown rate is 27.1 percent and its suburban 25.8 percent, while Oklahoma City was at 24 percent downtown and 21.7 percent in the suburbs.

But the pain is not confined to the sun and energy belts. Cincinnati registered 15.4 percent downtown and 17.2 percent in the suburbs, while Seattle showed 14.4 percent and 20.3 percent.

The markets with the least overbuilding are predominantly those where local governments make it hardest to build. Lower Manhattan's rate of 7.1 percent was second-lowest in Coldwell Banker's survey. Other downtowns with lower rates were Boston at 8.7 percent and San Francisco at 9 percent. These cities have tight regulations on development.

A survey of 33 markets by Urban Investment and Development Co. of Chicago found most had many years' supply of unleased new space, based on historical absorption rates. Indianapolis had enough office space to handle all the growth likely for the next 6.8 years; San Diego has a 5.3-year supply; Fort Worth, five years.

According to Urban Investment's data, 218 million square feet of office space have been built since 1980 or are under construction. All of the 1970s, by contrast, saw only 196 million square feet built. About 30 percent of all office buildings built since 1950 have been completed or started since 1980, the firm found.

In this environment, tenants are often able to obtain such concessions as months of free rent or even part ownership of the buildings.

Robert H. Gidel of the Abacus Group, a commercial mortgage banking firm here, observed recently about Washington: "I'd say that in the entire metropolitan area, every leasing deal being made has some kind of concession in it.

"One of the assumptions in the prospectus for the National Place complex at 14th and E streets NW, where a two-thirds interest was syndicated this fall for $60 million, was that all leases signed in 1984 will include six months' free rent."

Gidel said he ran across a building in Denver that "was 100 percent leased, and the rental income did not even cover the operating expenses. You figure operating expenses of maybe $6 a floor. That means that about 80 percent of that building is not paying any rent."

In the past, vacancy rates of this magnitude would have touched off waves of foreclosures. What's different this time? Most industry observers point to money. Deregulation has played a major role in this.

"We were trustees for years," Herschel Rosenthal, president of Flagler Federal Savings in Miami, said recently of the savings and loan industry. "Now they're saying, 'Look, I want you to be an entrepreneur, right, and go into other things' . . . . What's an entrepreneur supposed to do? He's supposed to make a profit."

But he does it by taking risks, and some "institutions are going hog wild," Rosenthal said.

Said Gidel: "If anything is driving this market, it's money. It's the fact that lenders have got more money than they know what to do with, and they're going to put it out."

In addition to loans, many institutions, ranging from savings and loans to insurance companies to pension funds, are becoming partners with developers putting up some, perhaps all, of the money for a share of what they hope eventually will be both operating profits and capital gains when the building is sold. Some of these types of institutions indeed have become developers themselves.

This is known in the business as "patient money," content to wait, even absorb some loss if necessary, in the belief that the building will lease up and be sold for a profit.

"If we had a credit crunch right now, you would see a severe real estate recession," Gidel said.

The tax benefits have created yet another source of money -- syndications. Investors in high tax brackets buy interests in buildings, usually as limited partnerships. The cash can reduce the amount of debt the building has to carry and also create a reserve to tide it over in periods of operating losses.

A building that seems thoroughly unappealing on a pre-tax basis often looks very nice to a 50-percent bracket investor. Even if it does not make money, it provides deductions while converting ordinary income to capital gains that can be realized -- and taxed -- at a later date.

The prospect of major changes in the tax laws is causing considerable consternation among investors.

"It seems pretty clear to me that real estate is probably the most heavily preferred industry under the present tax system . . . and that, therefore, almost any change is going to be adverse," James W. Wetzler, deputy staff director of the congressional Joint Committee on Taxation, told the National Apartment Association recently. "On the other hand, if there isn't any tax reform and they end up just increasing rates with a surcharge, well then, real estate wins because that just exacerbates whatever distortions in favor of real estate exist under the present system," he said.

The other large source of money is foreign investment, particularly institutions, which may provide the ultimate in patient money.

Foreign institutions "have long-time horizons, 10 years, if not 15 to 20," said consultant Apgar. Even though a property's return may be low -- even negative at first, and low by U.S. standards over the entire investment term -- it still can turn out better than what is available in the institution's home markets.

Added Gidel: "If you look at the sales of buildings in downtown Washington in the last three years, probably 80 percent of them are offshore foreign money. And I think that is going to be of even greater significance in the future.

"These buildings are going to turn around," Gidel said. And, in the meantime, the vacancy rate in Washington, at least, is spread around so that "no one is really out there dying."