After three years of stock market famine, waves of corporate scandals and government investigations, the federal tax bill now moving through Congress could be a badly needed shot in the arm for Wall Street. The compromise $318 billion tax cut, which Congress is expected to approve Friday, would help the securities industry by encouraging wealthy investors to start putting money back into the stock market, analysts say. In reducing both the tax on corporate dividends and long-term capital gains to 15%, experts say it should coax some investors from the sidelines. And any revival in the retail market is good news for Wall Street, because it translates into additional brokerage commissions and a renewed appetite for initial public offerings. But not all Wall Street firms will benefit equally from the tax cuts, which slashes the tax on dividends from about 39% to 15% and trims the long-term capital gains tax from 20% to 15%. The firms standing to gain the most are big brokerages that cater to wealthy investors who tend to own more conservative investments for longer than a year. That means firms like Merrill Lynch ( MER), Morgan Stanley ( MWD) and Charles Schwab ( SCH) will be the big beneficiaries of Washington's tax-cutting largess. On the other hand, the cuts will mean little to the hyperactive investors who are the main clientele of online brokerages like E*Trade ( ET) and Ameritrade ( AMTD). They tend to favor non-dividend-paying companies and are often in and out of trades in hours, never mind years. "My gut feeling is it will not have as big of an impact for an E*Trade or an Ameritrade as for a Schwab or a Merrill, which have bigger accounts and more buy-and-hold investors," said Richard Repetto, a brokerage analyst with Putnam Lovell Securities. Additionally, many investors also will not benefit from the Wall Street-targeted tax cuts.