President Reagan signed a bill yesterday that will put banks and savings and loan associations in competition with high-interest money market funds for billions of dollars in savers' deposits.

"This bill is the most important legislation for financial institutions in the last 50 years," Reagan said in a ceremony in the Rose Garden, surrounded by sponsors of the measure.

The bill, hailed by Reagan as an "historic reform" and the first step toward comprehensive financial deregulation, will allow banks and thrift institutions to offer deposit accounts at market interest rates, with limited checking account features and no withdrawal penalties.

Unlike the money markets, the accounts will be federally insured.

At the same time, the law will allow thrift institutions to make commercial loans.

Banking analysts say the law should allow banks and thrift institutions to lure money from the money markets, which now have about $200 billion in assets.

That, in turn, should make more money available for mortgage lending.

"It provides a long-term solution for troubled thrift institutions, it's proconsumer, granting small savers greater access to loans, a higher return on their savings and, when combined with recent sharp declines in interest rates, it means help for housing, more jobs and new growth for the economy," Reagan said.

"All in all, I think we hit the jackpot," he added.

The bill gives the industry 60 days to offer the new deposit accounts. The Depository Institutions Deregulation Committee said Thursday that it will attempt to approve the new account proposal before a scheduled Dec. 1 meeting.

Industry lobbyists have been pressing the regulators on the committee -- which include the Treasury Department, the Federal Reserve and the Federal Home Loan Bank Board--to act sooner rather than later.

That would help federally insured institutions capture the more than $31 billion in maturing All Savers certificate deposits that otherwise may escape during October and November to the money market mutual funds, the stock market or become general consumer spending.

DIDC members have said the minimum deposit for the new account probably will be $5,000. The legislation allows only three withdrawals a month from the new account without penalty.