-- Nine months after allegations of improper trading first rocked the mutual fund industry, regulators and industry experts agree the investigation into predatory short-term trading is winding down.

More than a dozen fund companies and brokerage firms have now paid more than $2.3 billion in fines, restitution and reduced fees to settle allegations that they improperly allowed some customers to engage in rapid trading at the expense of long-term investors.

More settlements are expected, including some with insurance companies that allowed similar trading -- called market timing -- in their variable annuity policies, and some with brokerage firms that improperly permitted customers to place same-day trades after the New York markets closed, regulators said. The largest unresolved case involves Invesco Funds Inc., charged in December with setting up an elaborate system for profiting from big customers who wanted to engage in rapid trading. Invesco's parent company has said publicly it is seeking to negotiate a settlement.

Regulators said that while they believe improper timing and late trading have now largely been uncovered and stopped, other questionable practices continue to flourish in the mutual fund industry.

The Securities and Exchange Commission staff is digging into issues including secret deals between brokerage firms and fund companies to push clients into particular funds; index funds that charge unusually high fees; and allegations that some funds are inflating the value of their underlying holdings. The SEC is also looking at conflicts of interest where money managers favored hedge funds over mutual funds or sent fund back-office business to firms in which they had a financial stake, the regulators said.

The SEC investigation "really extends into every aspect of the mutual fund business," said Stephen M. Cutler, who heads the enforcement division. "On late trading and timing, I believe we've broken the back of that set of issues, [but] we're not yet through the middle innings when it comes to some of the other mutual fund issues."

"We're really at the stage where it's not the new cases that are interesting but rather the possible remedies," said New York state Attorney General Eliot L. Spitzer, who brought the first trading case. "We've framed the issue already. Now it's up to the policy makers to decide what to do."

The SEC staff has put forward a raft of new rules and proposals aimed at strengthening fund boards, preventing improper rapid trading and forcing brokers and fund companies to tell investors more about the fees they charge.

But some are running into heavy opposition from industry groups who argue -- depending on the particular issue -- they will cost too much, be inefficient and create unnecessary burdens for investors and fund managers.

The Securities Industry Association, which represents brokers, has heaped scorn on a plan to provide customers with a personalized point-of-sale disclosure about the fees and commissions they would pay on a particular fund. The SIA wrote in a comment letter that there was "no logical justification" and that the SEC's plan would cost $2.7 billion a year, substantially more than the industry's annual profits from mutual fund sales each year.

The mutual fund trade group Investment Company Institute has been more polite so far. Its new president, Paul Schott Stevens, said: "We support the thrust of where the commission is going. We're just suggesting they trim the sails a bit."

Nonetheless, the group is lobbying hard against one of the SEC proposals, a plan to require that chairmen of mutual fund boards of directors be independent of management. The SEC will vote on that issue June 23. While the proposal is expected to pass, there is likely to be opposition from at least one commissioner.

All in all, said University of Mississippi law professor Mercer E. Bullard, who runs a shareholder advocacy group, "the industry has gotten off pretty light. I'd like to see some real reform, but the SEC hasn't done very much."

Bullard said he particularly wants regulators to rewrite the rules for the marketing fees that many funds charge their investors. Originally envisioned as a way to pay for advertising to attract new customers, they've become a backhand way of paying brokers.

Stevens predicted that his industry will continue to feel regulatory pressure for a long time. "With $7.5 trillion under management, the spotlight will never go away and a part of me thinks it shouldn't," he said.

Staff writer Carrie Johnson contributed to this report.