In testimony so alarming it prompted curses from a priest, executives from two big oil companies said yesterday that the oil industry will probably not produce as much heating fuel as the government considers necessary by the start of next fall's heating season.

Edward F. Wagner, a vice president of Atlantic Richfield (Arco), told a House hearing that he expects total reserves of heating oil to reach no more than 200 million barrels by Oct. 1, well under the government's target of 240 million barrels.

Charles F. Tebo, an analyst for Cities Service (Citgo), said his firm, a major supplier of heating oil to homeowners in the Northeast and Mid-Atlantic region, said his firm will be able to sell only 50 percent of last year's volume in October, November and December and 90 percent in January and February.

The Executives' forecast came as Assistant Energy Secretary John F. O'Leary told House members that the industry could meet the 240 million barrel goal without legal intervention by the federal government.

Officials from two other oil companies, Exxon and Shell, agreed with O'Leary in testimony earlier this week, saying the heating oil reserved would be adequate by October.

The confusion and uncertainty generated by the conflicting predictions was evident yesterday among the members who gathered to hear the Arco and Citgo executives' testimony.

"I just want to shout (expletive) at these oil guys," erupted Rep. Robert F. Drinan (D-Mass.), a Jesuit priest.

"Who are we supposed to believe? Are the 90-year-old ladies in my district going to have enough heating oil this winter?"

In the past two weeks heating oil has burned even hotter than gasoline as a source of controversy in the congressional committees dealing with energy. Yesterday's hearing was a joint production of three House sub-committees, an organization rarity that reflects the growing concern about the size of the nation's heating oil reserves.

A Carter administration memo that was leaked to Congress last week painted a severely pessimistic picture of the heating fuel situation, suggesting that fairly drastic steps will be needed to reach the 240 million barrel point.

Since heating oil is produced from the same raw material - crude oil - that is needed to make gasoline and diesel fuel, the oil industry will have to curtail production of the latter fuels to assure adequate heat this winter. That could lengthen lines at gas stations around the country and tighten a diesel shortage that already has farmers and truck drivers angry.

Wagner, of Arco, said yesterday that stepped-up heating fuel production now to meet the winter need will require "an additional reduction of about 7 percent in gasoline supplies over that [shortage] we are presently experiencing."

Both Wagner and Tebo, the Citgo officials, said their companies had received conflicting signals from the Department of Energy earlier this year as to whether they should emphasize production of gasoline for consumption now or heating oil to store for next winter.

Since about eight weeks ago, however, they have received fairly clear direction - although no mandatory order - from the department to concentrate on heating oil, the executives said.

But neither company seems to be rushing to do so.

Tebo testified that Citgo will "maximize" production of heating fuel beginning next month. After the hearing, however, he said that promise did not mean the firm will produce the maximum quanity of the fuel.