R2D2, alias CAD/CAM, is hurrying out blueprints and tools

''Back to the drawing board,'' engineers used to say. Now, it's more likely to be: ''Back to the CAD/CAM.'' Your watch, your car, your TV. An engineer designs all these products, and probably uses CAD/CAM (computer-aided design/computer-aided manufacturing) to do it.

CAD/CAM is doing to factories what the word processor has done to the office - drastically increasing production while cutting costs and time. It eliminates the ''repetitious drudgery work'' in mechanical, civil, architectural, and electrical engineering, leaving more time for creativity.

Like so many other high-tech areas, the CAD/CAM industry is growing so fast it can barely keep up with itself. What was a $900 million industry in 1980 will likely hit $5.8 billion by 1986. So says Bud Kocher, senior consultant heading up a CAD/CAM study by INPUT, an international consulting firm for the information industry.

The mouthful of words behind the CAD/CAM acronym really isn't as complicated as it sounds. The CAD part simply refers to computerized design of buildings, circuit boards, airplanes, bridges, tools, other computers, ad infinitum.

Without CAD the process goes something like this: Designer hands sketches to drafter; drafter develops drawing; hands technical information to departments for analysis; departments pass information to keyboard operators, who punch it into computer for more analysis. Computer detects errors, suggests solutions. Computer information handed back to original designer for review.

There are obvious problems with this method - it often takes months for results to get back to the designer, and the chance for errors increases as data change hands.

With CAD, the process can stop with the drafter. The system replaces the drafting board with an electronic tablet and pen and a video screen. As the drafter draws electronically, he can see his designs - solid or 3-D, color or black and white, cross section or head on - take shape on the video display screen. Duplicates come with a single command, errors are corrected, better designs suggested.

Compared with CAD, which is 10 years old, CAM is still a toddler. Using CAM in manufacturing means pulling the design from CAD and transposing it onto computer tape so the computer can feed instructions to a lathe, which then cuts a tool or part. These are regarded as significant steps toward the automated factory of the future.

''We still have to learn how to utilize CAD,'' says Jim Carr, a spokesman for Computervision Corporation, the country's No. 1 turnkey CAD/CAM vendor. ''The CAM end won't really come into play until the last half of the decade, mostly because of technology and money.''

Hundreds of manufacturers are already using CAD/CAM. General Motors and Boeing both anticipated the trend and were involved from the start. It is now indispensable to both companies. At GM, an experienced user of CAD is five times as productive as a conventional drafter, says Art Temske, director of corporate engineering at GM's computer coordination division. In some smaller companies, productivity can increase tenfold. ''There are some designs today that you just couldn't do without CAD/CAM,'' INPUT's Mr. Kocher says.

The surge toward CAD/CAM in manufacturing can mean only one thing for its makers - profits.

In the big league stand six major vendors of ''turnkey systems'' - Computervision Corporation, Applicon Inc., Calma (acquired this year by General Electric), Auto-trol Technology Corporation, Gerber Scientific Instruments Company, and Intergraph Corporation. The task for the turnkey vendor, who usually buys hardware elsewhere, is to supply the whole CAD/CAM shebang: central processor, graphics processor, disk drives, desktop terminals, plotters, software, service, and training.

In 1978, Computervision pulled in profits of $4.8 million on revenues of $48 million. Since then, profits have nearly quintupled and revenues quadrupled.

Applicon, No. 3 in sales and soon to be acquired by the French company Schlumberger Ltd., figures its annual growth rate will be ''better than 50 percent'' over the next five years. David Barber, vice-president of marketing for Applicon, which is on Route 128 near Boston, admits: ''We burn a lot of cash and Schlumberger will increase our resources.'' High interest rates and the recession, however, have recently pushed earnings back slightly.

CAD/CAM is one area where US manufacturers still dominate. According to Dataquest, a California high-technology research firm, US vendors command 70 percent of the world market.

The specialty of turnkey vendors is not to specialize. ''Fortune 1000 companies are much more interested in generalized software to perform mutliple-oriented disciplines,'' Applicon's Mr. Barber says.

Such firms can outfit huge workshops with systems each serving four to six work stations and costing $300,000 to $500,000 apiece. In some cases, a system pays for itself in less than a year, though the average payback time is 12 to 14 months.

One problem for the vendors and customers, though, is communication. Differing brands of computers can't exchange information, and manufacturers often use more than one brand. Just this fall, the National Bureau of Standards came to the rescue with a format for information sharing between various systems - a format that is beginning to catch on.

But the demand for specialized software and CAD/CAM minicomputers costing under $100,000 is skyrocketing. ''There were less than 10 low-end companies (those selling CAD/CAM computers for less than $100,000) prior to a year ago,'' says Dr. Timothy Gauhan, vice-president of design and manufacturing automation at Dataquest. ''This year between 15 and 20 new vendors started up.''

But computer analysts, top turnkey vendors, and even ''low end'' vendors have this advice for entrepreneurs: Specialize your software or you won't be able to compete; and once you become successful and noticed, watch out - you're acquisition material.