Sebastian Dovey, a managing partner at Scorpio Partnership, a wealth consulting firm in London, said that “we have not seen huge amounts of movement” of American money out of Swiss banks.

The current penalty for this type of failure to disclose assets is up to 50 percent of the highest annual balance of each account for each of the last three years  an amount that can quickly wipe out an investor and still leave him owing taxes and interest.

Investors who come forward before Sept. 23 face a reduced penalty, of 5 percent to 20 percent, depending in part on whether the wealth was inherited. They will also be hit with the penalty just once, on the highest balance in the accounts during the last six years.

The Justice Department has opened criminal investigations of 150 UBS clients, and is likely to bring more indictments on top of the four it brought in recent months. Only clients who are prosecuted are likely to have their names become public.

The landmark settlement is expected to provide a road map for the I.R.S. as it tries to clamp down on tax evasion by Americans who use offshore accounts.

Smaller Swiss banks are still helping clients hide billions of dollars through complex structures in offshore havens in the Caribbean, Panama, Luxembourg, Singapore and Guernsey in the English Channel. The crackdown is casting a spotlight on the network of lawyers, accountants and advisers who help underpin the Swiss private banking industry by steering clients to such banks.

An American official, who spoke on condition of anonymity because he was not authorized to speak publicly, said this week that the Justice Department was preparing criminal cases against some of the Swiss agents and intermediaries who set up offshore entities for clients and funnel their money to private banks. They take a referral fee in the process  sometimes up to 50 percent, according to a former UBS private banker.