WASHINGTON - Mutual fund companies such as Fidelity Investments and Vanguard Group would have to disclose stock holdings more frequently under a new rule being developed by the Securities and Exchange Commission, agency officials said yesterday.

The draft proposal, on which the SEC is to vote later this month, is supported by investor advocates and opposed by the mutual fund industry. Harvey L. Pitt, the lame-duck SEC chairman, recommended the change after accounting scandals at Enron Corp., Global Crossing Ltd. and other companies, agency officials said.

"This plan would allow people to make better judgments about investments in particular funds," said Paul F. Roye, director of the SEC's Investment Management Division. "If my fund owns Enron stock, for example, I might want up-to-date information about the extent of these holdings, so I can consider whether to change funds."

The government is trying to boost investor confidence after disclosures of corporate fraud helped push the Standard & Poor's 500 index down 20 percent this year.

For example, Congress has ordered the formation of an accounting oversight board to discipline accountants and inspect firms. The SEC also has proposed making mutual fund companies disclose their votes in corporate proxy contests on issues such as executive pay.

SEC rules now require mutual funds to disclose stock and bond holdings every six months. Roye declined to say how often funds would have to reveal investments under the SEC plan.

Investor advocates such as the Consumer Federation of America have asked the SEC to make funds disclose holdings every month.

SEC staff plans to submit the proposal to commissioners this month, said Cynthia M. Fornelli, deputy director of the SEC's Investment Management Division. Commissioners will vote on whether to issue the proposal for public comment before deciding on final adoption.

"The industry needs more frequent disclosure," said Geoffrey H. Bobroff, a lawyer and fund consultant in East Greenwich, R.I. "That said, I'm not sure how much difference it will make, since no one knew about Enron's problems till it blew up."

Pitt said last month that he would resign after bipartisan criticism of his handling of the appointment of former FBI director William H. Webster to chairman of the new accounting oversight board. Pitt is staying as SEC chairman until a successor is named.

The SEC plan comes as U.S. stock funds have been losing money and many people have switched investments from stock to bond funds.

About 52 percent of U.S. households have money in mutual funds, with $2.66 trillion invested in stock funds, a 14.5 percent decline over the 12 months preceding Oct. 31, according to the Investment Company Institute, a mutual fund trade group. Assets in bond funds have increased 15.5 percent, to $1.08 trillion, during the same period.

Fidelity and Vanguard Group, respectively the No. 1 and No. 2 mutual fund companies, both expressed concern about SEC efforts to require more frequent disclosure of portfolio holdings. The two companies disclose each of their fund's full portfolios twice a year.

Scott Beyerl, a Fidelity spokesman, said traders might be able to exploit more frequent fund disclosures. These traders could "front-run" the trades of a given Fidelity fund by buying the stock that the fund is in the process of buying, and selling shares that the fund is selling.

"Our disclosure policy reduces the likelihood of speculation on trading of securities by Fidelity funds that could adversely affect the price we receive or pay for the purchase and sale of securities," Beyerl said. Fidelity had about $732 billion under management as of the end of September.

Vanguard tried issuing quarterly statements in the late 1980s but changed back to twice-a-year disclosures after receiving investor complaints, Vanguard spokesman John Woerth said.

"It got to be costly, and shareholders asked us to stop sending them so much mail," Woerth said.

Each quarter, Fidelity discloses the 10 largest investments of each fund, and Vanguard does so monthly.

The Investment Company Institute urged the SEC to reject the petitions for more frequent disclosure.

Franklin Templeton Investments, the fourth-largest fund company, and Putnam Investments, the fifth-largest, disclose holdings four times a year, spokesmen for those companies said.