A divided Securities and Exchange Commission is expected to approve a plan today that would alter the way mutual funds are governed -- a far-reaching measure that investor advocates said could be the first step in lowering fees and preventing future trading abuses.

The five-member commission is likely to vote 3 to 2 in favor of a provision that would require the chairmen of boards of directors at mutual funds be independent of management, according to agency officials who asked not to be named because the deliberations so far have been private. The plan also would require that at least 75 percent of board seats be filled by independent directors.

The initiative has been fought by some of the nation's biggest fund companies, including Fidelity Investments and Vanguard Group Inc., whose chief executives also hold the positions of chairmen of their funds. Opponents say there is little empirical evidence to support the idea that board chairmen with management ties fail to consider the interests of average investors.

But since trading abuses and other problems in the $7.5 trillion mutual fund sector were uncovered by regulators last year, support for changes to the industry's operating practices has been mounting.

One of the plan's biggest champions is SEC Chairman William H. Donaldson, who said it would resolve potential conflicts of interest over fees and other thorny issues that come up when managers serve as chairmen of fund boards. Donaldson described the situation in a speech last weekend as "having to serve two masters."

New York Attorney General Eliot L. Spitzer's office, which first uncovered the problem of predatory short-term trading and other abuses at mutual funds last year, strongly supports the SEC proposal. Spitzer has insisted that fund companies seeking to settle improper trading charges install independent chairmen as part of any deal.

"There's not going to be significant reform in this industry until we get independent boards fighting for change," said David D. Brown IV, who heads Spitzer's investment protection bureau. "The way it's set up now is crazy. The president of the fund management company is president of the board that's hiring [his firm]. He's on both sides of the table."

Rep. Michael G. Oxley (R-Ohio), who chairs the House committee that oversees the financial markets, declined to comment yesterday, citing the impending vote, but in the past he has come out in favor of the proposal and pointed to the case of Richard S. Strong.

Strong, who owned 85 percent of Strong Capital Management and chaired the Strong fund boards, settled civil charges last month by paying $60 million and personally apologizing for letting investors down. Regulators said Strong made 1,400 short-term trades in funds he oversaw, netting him $1.8 million at the expense of the investors he was supposed to protect, Spitzer's office said.

Eric D. Roiter, general counsel of Fidelity's mutual fund arm, said in an interview that the company's operations would change little if the SEC proposal is approved, since Fidelity for years has given independent board members the power to set the agenda and make other key decisions.

"What we are concerned about is a very troubling inference that can be drawn from what the SEC is doing: that the government knows better than independent directors and that, by elevating one type of director, you necessarily are denigrating the fiduciary status of a management director," Roiter said.

Earlier this year Fidelity floated an alternative to SEC officials. The Fidelity plan would allow mutual fund boards to name independent chairmen or, if a chairman were affiliated with management, would ensure that each board committee was controlled by an independent director and that independent board members had sole power for setting the agenda. That alternative plan may come up at today's meeting, according to two sources involved in the dispute.

University of Mississippi law professor Mercer E. Bullard, who runs a shareholder advocacy group, calls industry opposition to the plan "greatly overblown."

"The opposition to this is largely about personal power and the chairmen having taken personal offense [at the idea] that their interests aren't aligned with shareholders," he said.

Bullard also said he didn't expect the rule would have much effect on well-run firms. "Will there be a benefit at Fidelity? Probably not. But at the firm where someone was considering something unethical, they might not [do it] if they knew the chairman was going to be watching. You regulate for the Richard Strongs of the world, not the [Fidelity chairman] Ned Johnsons."

Today's SEC proposal would not affect another aspect of fund boards that has drawn criticism from some experts and consumer groups: that most fund companies use the same board for all of their funds. That means a single board may oversee as many as 250 funds. Critics say that structure limits the amount of time the board can spend on each fund and may make the directors reluctant to make waves over a single fund's problems.

In addition, opponents of the plan argue, there is no clear correlation between management-led boards and the scandal that has plagued the fund industry since last fall. Putnam Investments, which paid $110 million to settle allegations that portfolio managers were allowed to make predatory short-term trades in the funds they oversaw, had an independent chairman for its fund boards. Fidelity and Vanguard have emerged from the probe largely unscathed.

Still Barbara Roper, director of investor protection for the Consumer Federation of America, said her organization has long fought for independent chairmen. "While we don't see it as a panacea that will solve every problem, we nonetheless think it's an important part of a comprehensive reform package," she said. "If you let the fund company chair the board, you minimize the likelihood that the board will act effectively to keep fees down and police other conflicts of interest."