The cement industry, which has been struggling with high costs and low profits for several years, suffered another setback during the third quarter of this year when efforts to maintain modest price increases collapsed, according to an industry analyst.

Imports from Europe, Mexico, South America and Asia have flooded the market, selling at prices far below those for the U.S. product. As a result, cement prices will stay down "for at least the next several years," predicted another analyst, Barbara T. Alexander, a Salomon Brothers Inc. vice president.

Bad news for the cement industry, however, is good news for the construction industry, including new housing, which uses nearly a third of all cement consumed in the United States. The "stability" of construction material prices, including those for cement, has been an "unusual and positive development" in the economic recovery, said Michael Sumichrast, chief economist for the National Association of Home Builders.

In previous recoveries, materials costs have run far ahead of inflation indicators, he said.

High production costs in new, energy-efficient cement plants, the low cost of foreign-made cement and the strength of the dollar abroad all have combined to make the U.S. industry vulnerable to imports, analysts say.

Spanish manufacturers, for example, are sending cement to the United States, unloading their ships, "filling up with coal from southern Illinois, taking it back to Spain where the coal is used to make more cement." This cement is then sent back to the United States, said Robert Roy, chief economist for the Portland Cement Association (PCA). The Spanish cement sells for $36.46 a ton at the dock, according to a Department of the Interior survey, $10 to $35 less than American-made cement in the East and Gulf Coast cities where much of it is sold.

In addition to the Spanish exports, "you've got Mexican cement coming into Texas, into the whole Gulf Coast and into California. You've got South Korean cement and cement from Australia and other countries in the Far East coming into the West Coast," said Alexander. Mexican cement now is priced "somewhere around $20 a ton less than U.S. cement," she added.

Although only about 10 percent of the cement used in the United States is imported, the foreign-produced material is used by American cement users "as a lever to keep domestic manufacturers from raising their prices or to beat them over the head to get them to lower" prices, Alexander said.

The one ton of foreign cement in every 10 tons used in this country could soon become one in two if domestic manufacturers do not keep their prices down, said another observer.

Prices of U.S. cement "have been bad for the last several years," but "stabilized" in the first three months of 1984, said Laurence H. Hirschhorn of First Boston Corp. Prices increased some in the second quarter, but "this evaporated in the third quarter" because "imports started to flood the market." Now prices are back down to where they were before the increases in early spring, he said.

Some domestic manufacturers have announced price hikes for January through March of 1985, according to Hirschhorn. "I'm optimistic" that the increases will take hold, "but I will tell you that I was shaken by what happened in the third quarter" of this year, he said. "That wasn't supposed to happen."

Lone Star Industries, the country's largest producer of cement, and Genstar are among the makers who have announced 1985 price hikes, while Kaiser Cement Corp. expects "pricing weakness" in its northern California markets during the early winter months, normally a seasonally weak period, according to Salomon Brothers. Kaiser reported losses of about 4 cents per share during the third quarter of this year on its U.S. business and an Indonesian manufacturing business in which it owns 43 percent. Counting one-time transactions, including a write-off of a Hong Kong cement operation, the company's loss was $6.90 a share.

Domestic manufacturers pushed for legislation restricting imports of foreign cement, but Congress adjourned last month without passing a bill.

Because foreign cement is such a small share of U.S. consumption, however, some cement industry officials profess not to worry about it.

"I tend not to take this import issue" too seriously, said Roy. The PCA, which represents U.S. and Canadian manufacturers, "takes a very neutral position." Canada, it should be noted, exports considerable quantities of cement to the United States annually.

Some domestic manufacturers, however, particularly those located close to a coast, "are very concerned" about imports, he said. Importers sell most of their product in or near the coastal cities, where it is unloaded because of the high cost of ground transportation.

The low value-to-weight ratio of cement makes its manufacture a regional industry in this country, with 60 percent of all cement produced shipped less than 100 miles from where it is made. About 95 percent travels less than 300 miles, according to the cement association's figures. Transportation costs can take as much as 25 percent of the price if cement is carried by truck or rail, Roy said.

Portland cement, named for the Isle of Portland because concrete made from it resembles stone found on the English island, makes up more than 90 percent of all cement used in the United States. Limestone or similar materials, such as shale, are ground into a fine powder, blended and burned in a kiln to produce cement clinker, the substance by which industry capacity is measured. The clinker ultimately is ground with gypsum to produce cement.

Major changes have shaken up the industry in the last decade, as the cost of producing clinker leaped from $50 a ton in 1974 to $125 to $175 this year.

Ironically, modernization, which was designed to save money, has contributed substantially to the cost rises. The industry, which is extremely energy intensive, is the nation's sixth-largest consumer of fuel. In recent years, new energy-efficient equipment has been installed, but for other reasons it is often expensive to operate.

"The surge in oil and natural gas prices that began in 1973 with the OPEC embargo was the impetus for a major reduction in the use of oil and natural gas" by the U.S. industry, according to a PCA report. Use of petroleum products and natural gas dropped by 92 percent and 88 percent, respectively, between 1972 and 1982, the report said. Coal and petroleum coke have been substituted.

But the new equipment has tended to be very large, making it difficult to adjust supply to demand, Alexander said. She used as an example a Kaiser Cement Corp. plant near San Francisco, where 12 kilns together had the capacity to produce 1.5 million tons of cement a year. The 12 kilns were replaced with a single new kiln that could produce the same tonnage. The problem is that this new plant "has two speeds -- on and off," she said.

Thus, "if you have the . . . option of running the plant full out or not at all, if you've got business, you run it full out," she said, often producing an oversupply that holds down prices.

" . . . Shutting one of these kilns down is not something you do in the evening when you leave, and turn it back on in the morning," she added. Starting up is a "long and involved process" that can take as long as a month.

In addition, much of the efficient new equipment was installed in plants located in the "growth markets," said Alexander. Many of these markets are near the seacoasts, where imports are most readily available.

Another major change in the cement industry is a dramatic growth of foreign ownership. Forty of the country's 143 cement plants are foreign-owned, accounting for 27 percent of the industry's production capacity. Ten years ago, of the 179 plants then in operation, only one was foreign-owned and produced 1 percent of all U.S. capacity, according to a Salomon Brothers report.

"Even more important than the ownership of domestic production capacity is the ownership of import terminals," which were "formerly controlled by domestic manufacturers to supply their customers during periods in which demand exceeded productive capacity . . . ," the report said.

Prospects for the future of American cement makers depend heavily on a continued U.S. economic recovery and the "pace of worldwide economic recovery," according to the report. Like some other observers, Salomon Brothers expects slow U.S. economic growth in 1985 and 1986, spelling a continuation of hard times in the cement industry.