America's biggest cities saw prices for existing homes fall from January through March and many other metropolitan areas experienced slower price gains, a real estate trade group reports.

The National Association of Realtors said prices for existing single-family homes fell in more than one-third of the 121 metropolitan areas surveyed, compared with the first quarter of 1990.This included New York, the nation's largest city, which saw prices decline 6.6 percent, to a median cost of $176,700; Los Angeles, down 3.6 percent, to $203,900, and Chicago, down 4.8 percent, to $107,500.

The median price means half of the homes cost more, half less. It ranged from $339,800 in Honolulu, up 4.6 percent from a year earlier, to $48,400 in Peoria, Ill., a 0.8 percent gain.

But while prices jumped in the Hawaiian capital, sales plunged 40.7 percent, the Realtors reported.

In an illustration of the effects of the recession on the housing industry, the Realtors also said sales of existing homes fell in 31 states and the District of Columbia, compared with the final quarter of 1990.

Still, sales rose 1.8 percent nationally based on advances in 16 states. Sales were unchanged in South Dakota and data was not available for Alaska and Maine.

All regions except the South registered gains. The Northeast was up 1.6 percent, to 620,000 units at an annual rate; the Midwest was up 7.7 percent, to a 980,000 rate, and the West posted a 7.5 percent gain, to 570,000 units.

Sales in the South were off 3.7 percent, to 1.3 million units at an annual rate.

Many economists believe the two-year slump in the housing industry bottomed out in the first quarter.

Harley E. Rouda, the Realtors president, said that while sales declined in January, they jumped the following month with the end of the Persian Gulf War.

Sales inched up again in March and Rouda said the Federal Reserve's recent interest rate cut "should provide the economy and the housing market with a potent shot in the arm to get things going again."

But the recession took its effect on housing from January through March as incomes fell and banks tightened credit, forcing down home prices in many areas as owners were unable to sell.

Nationally, the median price slipped 0.5 percent, to $95,400 - the second quarterly drop in a row. Prices also dipped 0.5 percent in the final quarter of 1990.

Regionally, median prices rose only in the Midwest, where they posted a 2.0 percent gain, to $75,700. They fell 5.1 percent in the Northeast to $138,800; 0.8 percent in the South, to $85,100, and 0.1 percent in the West, to $141,400.

Massachusetts communities posted the biggest quarterly price decline. The median price of existing homes in Boston dropped 8.7 percent, to $161,900, while in Worcester prices tumbled 10.6 percent, to $131,200 - the steepest plunge in any metropolitan area of the nation.

In addition to declines in Boston and the nation's three biggest cities, home prices also fell in Anaheim-Santa Ana, Calif., down 2.5 percent to $237,600; San Francisco, down 6.6 percent to $244,800; Hartford, down 6.8 percent to $146,400; Dallas, down 4.1 percent to $86,100, and Miami, down 2.3 percent to $87,900.

The Realtors said prices rose the most in smaller, less expensive cities. Boise, Idaho, for instance, recorded the biggest gain - a 22.5 percent increase to $82,200.