"Take your money and go."

That's the message being sent by Fidelity Investments, the nation's largest mutual-fund company, to investors who switch their money in and out of its stock funds based on the advice of market timers -- professionals giving advice on when to buy or sell securities.

Fidelity's decision to force these investors to leave their funds is in no subtle way directed at Fidelity investors who subscribe to Fabians' Telephone Switch Newsletter of Huntington Beach, Calif., which uses market statistics to tell investors when to buy shares in stock funds or move their cash back into money market funds.

Their departure could cost Boston-based Fidelity, which manages $100 billion in assets, between $100 million and $200 million. But the presence of the so-called "switchers" is so costly and disruptive to other Fidelity investors that it is well worth the price, according to William J. Hayes, senior vice president at Fidelity.

Fidelity's decision to get rid of switchers represents the most vigorous move yet in the industry against the coordinated, mass movement of money that occurs when the market timers believe various statistics signal a shift in the market's direction.

The Stein Roe funds, which manage $3.5 billion, took similar action in the spring. Other mutual funds have limited the number of times an investor's money can be moved back and forth in a specific period of time.

Hayes said Fidelity used its computers to identify investors who appeared to be following the pattern of Fabian switches.

Fidelity decided it was better off without these investors because when thousands of people simultaneously move large amounts of money in or out of a stock fund, it can force the portfolio manager to buy when prices are rising and sell when prices are falling -- practices that are costly to the fund and all of its investors.

Mass switching, Hayes said, raises commissions and operational costs and adversely affects a fund's performance.

In March, when the Fabian newsletter issued a buy signal for the $250 million Fidelity Contrafund, Fabian switchers poured $50 million into the fund before Fidelity shut the door.

If it hadn't stopped the flow, Hayes said, the switchers might have doubled the size of the fund within a short time. Several days later, Fabian issued a sell signal for the Contrafund, creating a mass exodus of funds.

"That was the last straw," Hayes said.

In a recent letter to "switchers," J. Gary Burkhead, president of Fidelity, wrote:

"When a large percentage of fund shares is moved suddenly, it can disrupt a portfolio manager's strategy and ultimately have a negative impact on fund performance."

Burkhead added, "If you intend to continue following newsletter market timing strategies, you should make arrangements to move your investment to another mutual fund organization before another 'switch' is called."

Burkhead said Fidelity will refuse to accept telephone orders from switchers who want to move money into the company's domestic growth or growth and income funds.

Dick Fabian, founder of the Telephone Switch Newsletter, reponded angrily to the Fidelity action, charging Fidelity with "blatant discrimination" against his 45,000 subscribers. He also denied that his investment signals disrupt the funds. "We are not market timers but strictly bear market avoiders and our switch signals are generally very infrequent," he wrote to Burkhead. The newsletter, he said, never recommends selling a stock fund unless it sees a "definable downtrend which has the potential of being a bear market."

Fabian's son, Doug, said that during the 14-year life of the newsletter, it had issued only 13 switch signals. There were none last year but several this year, he said. Readers, he said, were told to sell in January, to buy and sell within a few days in March, to buy in May and to sell and move into cash in early August.

"They couldn't have picked on a better time to pick on me," Doug Fabian said. "We could be out {of stocks} for an extended period of time."

Fabian said the next issue of his newsletter would drop the Fidelity funds from its recommended list.

One of the events that triggered Stein Roe's decision to ban switchers came last January, when the Fabians' newsletter advised its subscribers to sell shares in the $250 million Capital Opportunities Fund. The result, according to a spokeswoman for the fund, was that $50 million, or 20 percent, suddenly flowed out of the fund.