[ No headline ]

A California newsletter has joined the ranks of those warning that Wall Street's love affair with high-technology stocks may be in for a stormy end. James McCamant and Michael Murphy, editors and publishers of the California Technology Stock Letter, based in San Francisco, hold that the high-tech group could be in for a pounding if the market turns south. ''If the market turns down 10 to 15 percent,'' says Mr. McCamant, ''these stocks could fall 25 to 30 percent in a couple of days.'' All it takes, he adds, ''is a little bit of bad news to shake things up.''

Reflecting this view, the newsletter's model portfolio - up about 95 percent since the publication's start in January of 1982 - is now 25 percent in cash. And, according to Mr. McCamant, it is ''on the edge'' of selling more stocks and increasing its cash hoard to 50 percent. Why?

''So you don't give back the gains,'' Mr. McCamant says. ''That's what performance is all about.''

Over the longer term, however, they expect to see the high-tech sector outperform the market. Over the next 10 to 15 years, in fact, they expect high technology to change the nation as much as when the railroads opened up the country at the turn of the century.

In the past, he concedes, the newsletter ($220 a year) has encouraged its readers to get into and out of stocks too soon. For example, last June it was advising investors to buy Apple Computer at $15 a share. Apple eventually bottomed out at about $11 a share. Then, as it was heading back up, the advisers told their clients to bail out at $30 per share. Apple has passed the $50 -a-share mark - and is still listed as a ''sell'' in the newsletter.

How do they decide it's time to sell? First, they set ''target levels.'' ''We generally look for a stock which will double in 12 months,'' Mr. McCamant says. He admits this strategy has its shortcomings in a bull market. After they had a ''double'' (the price up 100 percent) in Emulex Corporation, buying it at $11.75 a share and selling it at $25, the stock kept rising, hitting $40.

''We generally look for value,'' Mr. McCamant quips, adding, ''Today, this isn't a universally popular pursuit.'' Both editors have been around long enough , however, to see the market make some investors millionaires and others paupers.

Mr. McCamant has been following high-tech companies since the mid-'60s and Mr. Murphy, entering the securities industry in 1968, eventually became a portfolio manager at Capital Research, a big money-management firm in Los Angeles. The two decided to begin the newsletter because most of the high-technology research was geared to institutions - not individual investors.

Their latest recommendation is Phone-Mate (OTC, $12.50 to $13 recently), which makes phone-answering machines and is expanding into the telephone business. They expect a large swing in earnings this year and are optimistic about the company, recommending that their readers sell the stock at $25 a share.

At the same time, they gave a ''disconnect order'' on Rolm Corporation, one of Wall Street's hot telecommunications companies. ''The stock has a lot of risk ,'' they conclude.