Assets of money market mutual funds rose last week by $252.2 million, reversing a continuous decline that began Dec. 1, 1982, as investors apparently chose the funds as havens while awaiting clearer trends in the stock market.

According to the Investment Company Institute (ICI), total assets now stand at $165.5 billion, compared with $231 billion at the funds' peak.

Funds open to individual investors showed a rise, whereas those limited to institutions registered a loss. Reginald Green, spokesman for ICI, a trade organization for mutual funds, said he thought the $413 million rise in general purpose funds was caused by individual investors' uncertainty over the stock market. "They took their money out of stocks and parked it in money funds with minimal risk while waiting to see if the market would continue to go down," he said.

As for institutions, which pulled $255 million out of money market funds last week, Green explained that they habitually do this when they can get a higher rate of interest on the underlying investments.

Money market mutual funds began registering weekly declines when banking institutions started paying high market interest rates on insured accounts. At the outset, promotional offers--as high as 20 percent interest in a few cases--lured away dollars by the billions. However, in recent months there has been an average difference of about one half percentage between the funds and the accounts.

The average interest rate on money market deposit acounts offered last week by banks was 8.4 percent, according to the Bank Rate Monitor in Miami. Donoghue's Money Market Fund Report yesterday reported the average for all money market funds was 8.24 percent, up from 8.22 percent. Donoghue's put the weekly gain at $295 million, for total assets of $162.6 billion.

Mutual funds assets have increased by 60 percent since last summer to $70.7 billion. Sales are currently four times as high as this time last year.