George Gilder is trying to be a visionary. Too bad the market is treating him like a tout.

An executive at the technology seer's

Gilder Technology Group

says the publishing company is discussing whether it should change how it releases its monthly

Gilder Technology Report

because the newsletter is driving outlandish gains in stocks it mentions. Evidence of that phenomenon was in abundance late this week, when a pair of tech stocks jumped more than 70% over two days following mentions in the report.

"We're pleased to have the attention," says Spencer Reiss, vice president of the Housatonic, Mass., company and editor of its

New Economy Watch

investor newsletter. "But it's a little frustrating. ... It's irritating, because we see our core audience as people who want to know and understand where and how the technologies are moving, and not people who just focus on a four-letter trading symbol."

Midas Touch

In the latest example of the monthly Gilder effect, first sighted in 1999, shares in two companies jumped nearly 50% Thursday. The stocks added still more Friday after Gilder wrote favorably about them in his February newsletter, which was published online some time after the market's open Thursday.

Terayon Communication Systems

(TERN)

, a cable-modem manufacturer about which Gilder has written several times, jumped 67 3/16 Thursday to close at 204 1/16. The jump was inspired by Gilder's comment that the company was "poised to repeat

Qualcomm's

(QCOM) - Get Report

remarkable success" in the field of CDMA. Qualcomm, you'll remember, rose more than 2,600% in 1999 on that very success. In addition, shares in

Xcelera.com

(XLA)

, about which Gilder was writing for the first time, jumped 61 to close at 190 after Gilder positively mentioned a subsidiary,

Mirror Image

, which has developed a system for speeding up delivery of Internet content. Friday the buying frenzy continued, with Xcelera adding 50, or 26%, to 240 and Terayon jumping 28, or 14%, to 232 1/4.

This isn't the first time that Gilder's words have had a salubrious effect on Terayon's price. In June 1999, the stock rose 28% to close at 41 1/2, in a move that

Dow Jones

attributed at the time to a mention in the

Gilder Technology Report

. Reiss says the first time the publishing firm really noticed an effect from the newsletter was a month later, when bandwidth provider

NorthEast Optic Network

(NOPT)

rose 67% in a single day after a favorable mention from Gilder.

Nothing Gold Can Stay

Not all subscribers to Gilder's $295-a-year newsletter are happy about the waves he's been able to make in the market. It's not that they're unhappy when the stocks he recommends go up; rather, they're angry because they don't even have time to take advantage of the recommendations before the stock moves, or that word of the picks quickly leaks out to nonsubscribers who haven't ponied up cash for Gilder's insights.

On the Gilder Technology Group's members-only Web site Friday, one subscriber, for example, complained that Gilder wasn't living up to promises on the Web site

www.forbes.com/subscribeindex , where people can sign up for the report -- promises such as "be the first to know which companies are on the right track and which ones to avoid." Added the poster, "How many of you feel you got this with XLA? How many of you feel you lost a big $ opportunity with XLA due to the failure of GTR to live up to this promise?"

Another poster wrote about the quickly spreading news, "It does raise the question of whether anyone should pay for something that soon becomes free to everyone."

Eye of the Beholder

And not everybody is convinced of the company-specific value of Gilder's insights. The passion with which daytraders apparently embrace Gilder's choices doesn't prove the value of his predictions, says Bill Frezza, general partner at

Adams Capital Management

, a venture capital firm specializing in telecom and information technology infrastructure. The short-term stock movement "has nothing to do with what's going to happen over the next three years."

Says Frezza: "George is great at the big picture and great at the long view. What George is terrible at is accurately forecasting what's going to happen in the next three to five years." For example, says Frezza, the adoption of cable modems such as Terayon's has no chance of being adopted as quickly as technology sold through national sales channels, such as 56K modems. Gilder is "always overoptimistic," Frezza says.

Traders or Investors?

In any case, the letter has its adherents. "In George's mind, he's writing for the buy-and-hold investor," Reiss says. "There's a small but significant group of peple who have realized that this market-moving thing is happening, and are playing it as traders, not investors." Gilder, who was traveling Friday, was unavailable for comment.

That appears to be a curse that Gilder has to live with -- people's reduction of his newsletter to the mention of names. In fact, the dense and dramatic newsletter -- February leads off with the question, "After the floods of bandwidth, who will greet the dawn and the dove?" -- aims to give readers the big picture about important trends in communication, not hot stocks to own.

Yet it's because Gilder has had a hot hand -- he was a booster of Qualcomm early on, for example -- that people are paying very close attention to the stocks he likes, and not necessarily the technotrends he sees.

"George has quite a following out there in the market," says Uri Landesman, chief investment officer of the

Fleck T.I.M.E. Fund

, a hedge fund specializing in telecommunications, the Internet, media and entertainment. "He's considered someone who is technically proficient enough to tell between value-added products and hype. ... It's tough to bet against the record that he's had recently."

Landesman -- who says his firm invested in Terayon, its biggest holding, starting about a year ago -- says the fund hasn't sold its position in the recent run-up, and probably won't. "If this really is another Qualcomm on the price-movement basis," he says, "there's a lot of upside."