As brokerage giants Morgan Stanley Dean Witter and Merrill Lynch prepare to offer online trading this year, some investors may be telling online and discount brokerages, "Don't just take my money -- hold my hand, too."

This week Morgan Stanley Dean Witter is expected to announce plans to offer online trading services to all its customers, even their high-tone clients, by integrating accounts with its Discover Brokerage unit -- the same group whose TV ads make full-service brokers seem superfluous. Morgan Stanley Dean Witter's plans come as no surprise, given Merrill Lynch's announcement last summer about its new online trading services, which the firm insists won't cannibalize its army of financial consultants. "We believed that once we announced we would have online integration, others would follow," says Merrill Lynch spokeswoman Susan Thomson.

Morgan Stanley Dean Witter is expected to offer several online trading services, varying by how much involvement the customer wants to have with a broker. Both Merrill Lynch and Morgan Stanley Dean Witter are pushing into a space that Charles Schwab and ETrade have dominated online, says Steve Franco, an analyst with U.S. Bancorp Piper Jaffray.

LITTLE HELP?Discount and Net-only brokerages for a while now have touted their ability to give clients freedom from high commissions and broker meddling. In the future, though, Mr. Franco says, "online trading alone will not be enough."

"The next wave of consumers coming online won't be as sophisticated as early adopters of online trading," says Dan Burke, an analyst with Gomez Advisors. Mr. Franco, Mr. Burke, and other analysts say that -- contrary to the belief that online financial services would replace live brokers -- financial advisory services are going to remain important to most consumers.

That doesn't mean firms like Ameritrade or Datek Online are in danger of losing their customer base to Merrill Lynch or Morgan Stanley Dean Witter. There will always be segmentation in the market, and there will always be people who choose an online brokerage based on whether it can provide fast and cheap trades.

THE PENDULUM SWINGS BACKWith more pervasive online trading, traditional brokerage customers are expected to get the online access they want, and have more control over how involved brokers are in the process. Consequently, the next few years are expected to see a remarkable jump in assets held by online brokerage accounts. Jupiter Communications says those accounts will increase from $415 billion at the end of 1998 to more than $3 trillion by 2003.

Even as online brokerage accounts increase in number and size, Gomez's Mr. Burke says, "The mainstream investor needs advice, and the pure online brokerage model is going to need more [financial advisory] support."

As consumers demand services other than quick and dirty trades, Jupiter predicts the revenues that online brokerages receive from transactions and commissions will drop over the next few years. Interest, fees, and other "non-transactional services" will represent 80 percent of total revenues by 2003, the consultancy says. Consequently, behemoth brokerages with big asset bases should fare better than smaller, pure-play Net brokerages over the long run.

Jupiter's September report, "Financial Services Online: Forecasts and Strategies for Acquisition, Retention, and Wallet Share," goes so far as to suggest that discount firms such as Datek, Ameritrade, and Suretrade will be pressured to provide broader product offerings and may even feel compelled to lower prices to the point where they'd lose money on each transaction -- making up for losses with advertising revenues. Nonetheless, Mr. Franco says that Net-based brokerages will keep adding services until they can provide at least 80 percent of the value that full-service brokerages provide.

ETrade CEO Christos Cotsakos made his mark taunting firms like Merrill Lynch and Morgan Stanley Dean Witter for being late to the online fray. The irony is that when those slower-moving giants finally lumber online, ETrade and other Net-only brokerage firms will see slip their first-to-market advantage. Then they'll be forced to offer big-brokerage services to keep up.