Prices for crude oil and heating oil yesterday dropped to the lowest levels since the late 1970s, pushed downward by an oversupply of both crude and petroleum products, industry analysts said.

The price for a cargo of heating oil in New York harbor fell to 65 1/2 cents a gallon yesterday. It had been 90.15 cents a gallon in the last week of November.

The price of the most commonly traded U.S. crude oil hit $24.11 a barrel yesterday on the New York Mercantile Exchange, where contracts for future delivery of crude oil petroleum products are bought and sold. The price had been as high as $30.43 a barrel on Nov. 25. (There are 42 gallons in a barrel.)

Both the heating oil and crude oil prices are the lowest since 1979, according to Peter C. Beutel, an analyst with Rudolf Wolff Futures Inc., a futures trading company that closely follows energy prices. If the decline in the value of the dollar since 1979 because of inflation were taken into account, today's energy prices would be substantially lower than those at the end of the last decade.

Most energy prices headed downward around Thanksgiving, following a decision by Saudi Arabia to boost production of crude oil significantly this winter. In November, increased shipments of imported oil began arriving in this country because of the increase in Saudi oil production, thus adding to an oversupply of oil and petroleum products.

The Saudis' announced determination to continue higher levels of oil production this spring and summer has knocked a psychological prop out from under oil prices, as well. A major price war is likely if Saudi Arabia does not cut production when the winter heating season ends and if other oil-producing nations attempt to maintain current production targets. In that case, oil prices could fall below $20 a barrel, Saudi officials and U.S. energy analysts have said.

The production plans of the major oil-exporting nations are the key to the equation, because the worldwide demand for oil products is expected to decline slightly over the next two years, according to an analysis by a major U.S. energy company. That projection shows worldwide crude oil demand at 45.6 million barrels a day this year and 45.7 million barrels daily next year, compared with a demand of 45.8 million barrels a day this year. The estimate has been made available to government officials and the press on condition that the company not be named.

The demand for oil is expected to be flat despite continued economic growth because of the effects of continued energy conservation.

Assuming other oil-producing nations outside the Organization of Petroleum Exporting Countries continue to pump oil at current levels, the level of OPEC production would have to be held at 15 million to 15.5 million barrels a day to match demand and maintain prices, the projection concludes.

But Saudi Arabia and other OPEC members are insisting on obtaining their "fair share" of the world market, which, by their reckoning, exceeds 17 million barrels a day, industry analysts said. It is that excess supply that promises to push prices down sharply later this year, unless either OPEC or the non-OPEC producers give ground.