U.S. computer makers, their in-baskets overflowing with orders from this country and overseas, are suffering from major shortages of a critical type of semiconductor that have caused slowdowns on production lines and delays in deliveries.

A number of smaller companies say they are facing a serious loss of business because they can't fill their orders in a timely fashion, and even some of the hottest operations in the high-technology field are feeling the pinch from the shortage of dynamic random access memory (DRAM) semiconductors.

"We could use more DRAMs. We could ship more products if we had them," said Scott McNealy, president of Sun Microsystems Inc., a fast-growing, six-year-old company that makes computer work stations.

Other companies "are just slowing down and are not able to fill orders," said Charlotte LeGates, communications director of the Computer and Business Equipment Manufacturers Association.

The shortages, furthermore, have been accompanied by substantial prices increases. At a meeting in Washington last week, one company reported paying $80 for an advanced form of DRAM that cost $12 a year ago, a participant said. According to a survey by Dataquest Inc., a Silicon Valley market research firm that compiles statistics on semiconductor use, the price of a less-advanced chip, purchased in large quantities, has risen close to $3 from $1.80 a year ago. Buyers are reporting a four-month wait for new orders, twice as long as last summer.

Semiconductors are the driving force of the information revolution. They are key components in the design, development and production of telecommunication systems and computers, and are increasingly being used in a host of everyday products ranging from inexpensive watches to automobiles. DRAMs, semiconductors that store information, often are called memory chips.

"There's a sheer critical lack of supply" of memory chips, said Ralph J. Thomson, senior vice president of the American Electronics Association. "It's very much the issue in the industry. We're seeing some very long faces" among semiconductor users.

Dataquest predicted that the shortages, which developed during the summer, will get worse before they abate.

"There will be a very tight supply through the second quarter {June}. The demand is high and the supply is tight," said Stan Victor, a spokesman for Texas Instruments, one of two U.S. companies that still make DRAMs. The other U.S. maker of DRAMs is Micron Technology of Boise, Idaho.

Japan, which is blamed for driving most U.S. companies out of the business in the mid-1980s by "dumping" chips in this country at less than their cost of production, now supplies 80 percent of the memory semiconductors used in the United States.

Some computer makers place part of the blame for the shortages, which are worldwide, on production cutbacks ordered by the Japanese Ministry of International Trade and industry (MITI) as a result of a 17-month-old U.S.-Japan semiconductor trade agreement designed to stop the dumping and increase U.S. sales in Japan.

But other industry analysts say the shortages are due to greater-than-anticipated problems as Japanese manufacturers switched to production of a more powerful new DRAM that holds 1 million bits of information. These "one-megabit" chips, the most advanced memory semiconductors now in production, are replacing 256K DRAMs that carry one-fourth as much information as the more powerful semiconductor.

"It's a generational change from the 256K," said Tai. Jack Wilson of Dataquest said the new technology is so tricky, involving the placing of microscopic electrodes in a three-dimensional manner on a tiny wafer of silicon, that Japanese factories are able to get usable chips from only 15 percent of each wafer.

"Every generational leap has been difficult, but this one has proven tougher for the industry than the industry expected," added TI's Victor.

He said that his company is producing 256K DRAMs at "record levels" in its Dallas plant, and that the one-megabit chips are being made in its Japanese factory, which expects to be hitting high volume by the end of March. Victor added that the firm is gearing up to start production in Dallas.

"There's a rational reason for people to invest in memory right now," he said.

Ward Parkinson of Micron Technology agreed that other companies could start producing DRAMs in America, but he said the only reason companies can't get memory chips is that they are unwilling to pay the price. "If they think they've got shortages, tell them to give me a call," he said. "But they'll have to pay the price."

Even with the shortage, U.S. companies are reluctant to reenter the business of making DRAMs. Despite trade sanctions President Reagan imposed on Japan last year, they say they remain unconvinced that the U.S. government will continue to enforce laws against unfair trade practices.

"The Japanese killed all the U.S. semiconductor companies," said Bill Tai, an analyst in San Francisco with the securities firm of Alex. Brown & Co. He said U.S. manufacturers lost $2 billion in those years as a result of Japanese dumping.

"Now that demand is starting to outstrip supply, the U.S. companies are afraid to sink money into new lines," Tai said.

"We are not anxious to get into that loss situation," said Charles E. Sporck, chairman of National Semiconductor Corp.

Industry experts said it would take a company two years and about $200 million to set up a DRAM production line. "In two years, where is the trade agreement?" asked Sporck. "There's not a high level of confidence that the U.S. government knows what it is doing about trade."

While the Reagan administration is exerting gentle pressure on semiconductor manufacturers to use the trade agreement with Japan to start producing DRAMs, Wall Street analysts generally back the industry's reluctance to get back into that field. One said that shares of any chip maker that announced plans to start a DRAM line would plummet because of the risk.

Nonetheless, pressure from chip users may succeed in getting manufacturers back into the DRAM business. AEA has been sponsoring a series of meetings to bring users and producers of semiconductors together to gain a common understanding of the problem.

One thing that appears to be emerging from these meetings is the realization that U.S. semiconductor users are too dependent on Japan as the major source of DRAMs. "We're trying to push the U.S. semiconductor makers to double their production of DRAMs to 40 percent" of the U.S. market, said an industry source.

McNeely of Sun Microsystems was even more specific. "Sun very much values its Japanese vendors and will continue to value its Japanese vendors," he said. "But we are actively looking to get second sources that are not Japanese."

He said he is looking to American or South Korean companies as new suppliers. "We consider all Japanese companies to be a sole source" because of the influence MITI has over the industry, McNeely added.

U.S. companies are also growing concerned because the Japanese suppliers of DRAMs and other chips are part of vertically integrated conglomerates that also make competing products such as mainframe computers, supercomputers, telecommunications equipment and work stations.

So far, the U.S. semiconductor industry has found no evidence that Japanese companies are keeping chips out of the United States to hurt their American competitors, said Daryl Hatano, director of international trade for the Semiconductor Industry Association. But the worries persist.

"The shortages are forcing the American users of these chips to take a real hard look at their sources of supply and to realize that they are dependent for critical supplies on companies that are, or are trying to be, major competitors," said Jack Wilson of Dataquest.

A chip maker said that his company is under "lots of pressure" from "very important customers who say they don't want to be dependent on the Japanese, who are competing with them in the systems area."

He said these customers tell his company, "If you want to be a major supplier to us you have to supply DRAMs." But he questioned whether the chip users will stop buying Japanese DRAMs when the shortage is over. "In a period of glut," he said, "competitive pressure will force the users to buy on price."