The Dow Jones Index and the Standard & Poor's 500 Stock Average have climbed 35 percent in the last six months and the Johnston, Lemon Index of 30 Washington-area stocks has gained 63 percent, but a new Washington investment indicator has outperformed them all.

It's called the Beltway Technology Index and since July 31, it's up 76 percent.

Created by Scott & Stringfellow Inc., the Richmond-based regional stock broker, the Beltway Technology Index is the first attempt to chart collectively the investment performance of Washington's emerging high technology industries.

Scott & Stringfellow Research Director Michael Mead chose 10 companies to represent the spectrum of local leading edge firms. He explains that in developing the index, "we have used a fairly broad definition of high technology, cutting across many fields of chemistry, electronics, computers, technical services and communications."

The Virginia firm, which has eight offices serving a region stretching from Norfolk to Winchester, recently began a bimonthly Beltway Technology newsletter devoted to Washington-area firms. Like many investors, Mead looks for companies close to home as potential investments. "In my research I found more and more companies in the Washington area that were involved in high-technology areas."

The 10 he chose to represent the region range from early learning curve outfits like CACI Inc. and Radiation Systems to that gestating giant, MCI Communications. Filling out the list are Atlantic Research Corp., BDM International, C3 Inc., Dynalectron, Flow General, Hazleton Laboratories and Penril. More companies may be added in the future, he said.

The Beltway Technology Index is by no means a comprehensive compilation of Washington's science and technology enterprises. Comsat is as far out as you can get, Advanced Technology Inc. ought to qualify on name alone and Planning Research, STSC and Scope could make the list, though they are more heavily dependent on government contracting. Half a dozen smaller firms could qualify, including Software A. G., Cerberonics and what is perhaps the highest-tech of the beltway wonders--Genex Corp., the Rockville genetic engineering outfit that recently went public.

You could argue, too, that MCI's spectacular growth is more the result of being on the cutting edge of communications deregulation than on the frontier of technology, but MCI recently placed the biggest order ever for state-of-the-art fiber optics equipment.

From an investor's point of view, the most important thing about a company is not how high its technology can reach, but how high its stock price will climb. On that criteria, the Beltway Technology Index is a solid success.

Mead said he expected the high-tech growth stocks to be "more volatile" than the stock market as a whole and that's proven to be true. The stocks show an extraordinary range of prices over the last year. Atlantic Research has traded over a range of $14 to $40; BDM from a low of $15 to a high of $44; CACI from $9 to $53; Flow General from $7 to $28. The trend lines have not been upward, as the fall of Flow General to the $12 range evidences.

But as a group, the Beltway Technology stocks have done just what growth stocks are supposed to do. Using July 31 as a base of 100, the index is up to 176 in just under six months. In the two-month period from Nov. 11 to Jan. 13, the index climbed from 159.93 to 176. The 10 percent gain compares with a 2.8 percent increase in the S&P 500, a 1.8 percent boost in the Dow Jones Index and a 5.2 percent climb in Scott & Stringfellow's broader index of regional companies.

What's important about the Beltway Tech Index, however, is not that Mead has picked 10 of Washington's high-tech, high-growth companies and tacked a buzzword on them.

Creation of the index reflects rather the growing realization that the Capital Beltway is the main street of one America's most important science, research and technology centers.

"The Washington area is becoming like Silicon Valley south of San Francisco and the Boston area," Mead contends. (Just to be safe, you could throw in the Denver-Boulder axis that's sometimes called Silicon Mountain and the Texas technology ranches around Dallas and Fort Worth.)

Scott & Stringfellow isn't the first investment advisor to discover Washington's high-technology companies. The local brokers--Ferris & Co., Johnston-Lemon and Wachtel & Co.--got in on the ground floor of many of the Beltway Technology issues. Baltimore's Alex Brown & Sons has set out to make a name for itself in high-tech stocks, with a series of research studies and seminars on investment opportunities in computers, communications and related subjects. Alex Brown has three dozen telecommunications companies on the program for a three-day seminar starting March 6.

Despite the surge of interest in the stocks and the surge in prices which that interest has produced, high-growth, high-tech companies remain high-risk investments. The gains in their stock prices in the last few months could be wiped out by the whims of a fickle stock market, a cut in government research funds or a promising research venture that proves to be a dry hole.

The Beltway Technology stocks, too, have to prove that they can match the performance of Washington companies that may be less glamourous but are equally upwardly mobile. Groceries, drugs, lumber and newspapers may not be as trendy as computers, gene-splicing and synthetic fuels, but tell that to investors who have taken their profits recently on Peoples Drug Stores, The Washington Post Co., Giant Food or Hechinger stock.