Fidelity Investments, the nation's largest mutual fund company, deliberately provided incorrect information on the value of its funds last week, causing newspapers to report that most Fidelity funds did substantially better than they actually did.

A Fidelity spokeswoman, Constance Hubbell, said yesterday that the fund management company had not been able to calculate the value of 166 funds on Friday because of a computer problem.

Rather than simply admit the problem, she said, Fidelity chose to report to the National Association of Securities Dealers (NASD) that nearly all of its funds had not changed in value Friday, a generally bad day in U.S. financial markets.

Ms. Hubbell first defended that decision, and said Fidelity had done it at least once before, during the 1980s. But late yesterday, after being told that a spokesman for the NASD said such an action would be a violation of its rules, she said she had been misinformed by other Fidelity officials regarding the company's policies. "It will never happen again," she said.

Barry Barbash, director of the Securities and Exchange Commission division that regulates mutual funds, said he had not known of Fidelity's action and did not want to discuss the incident directly.

When investors buy, or sell, fund shares, the pricing of the transaction is normally based on the next closing price of the fund, in some cases after adjusting for a sales charge. So an investor who placed an order with Fidelity after 4 p.m. Thursday, and before 4 p.m. Friday, got the closing price Friday, and would normally be able to learn what that price was by looking in the newspaper over the weekend.

But Fidelity said yesterday that it was not honoring those prices. Instead, it is charging the actual prices, a fact that will come as a shock -- in some cases a pleasant one and in others a disagreeable one -- to many who bought or sold Fidelity funds before the close Friday.

In many cases, the differences are substantial. The Fidelity Magellan Fund, the largest stock fund in the country, was reported in many weekend newspapers -- including The Sun on Sunday -- as having risen 95 cents, or 1.4 percent, during the week. That performance was better than many of its competitors. In reality, factoring in its actual performance Friday, the fund was up just six-tenths of 1 percent for the week.