Partly as a result of its comparatively lower prices, Exxon Corp. has become the leading marketer of gasoline in the United States for the first time in the company's history, an oil industry survey reports.

Using data for the first three quarters of 1970, the independent Lundberg Letter said that since 1978, Exxon jumped sharply over the previous industry leaders, Shell Oil Co. and Amoco, and can be expected to come out on top for the year once fourth quarter figures are in.

During the first three quarters of 1979, Exxon has 7.77 percent of the U.S. gasoline market; Amoco, 7.31 percent; and Shell, 6.97 percent, according to the newsletter.

In its year-end report published Friday, the North Hollywood, Calif.-based newsletter said that Exxon's new preeminence was brought about by two main factors, pricing and allocations. During the third quarter, Exxon's retail gasoline prices were an average of 2.4 cents a gallon below the average for the major oil companies, while for the same perios, Amoco's were consistently above average and Shell's about average.

"This pattern intensified in the fourth quarter," said the survey, noting Exxon's retail prices dropped to 4.6 cents a gallon below the average for the majors, while Amoco's and Shell's were above the average for the same period.

The survey also reported that Exxon was able to allocate higher total gasoline percentages than its competitors.

Under the federal allocation system, oil companies must report monthly how much gas they will deliver compared to comparable base periods. Durng the past six months, Exxon allocated 96.5 percent of the amount delivered during a comparable period one and two years ago, while Amoco's and Shell's allocation averaged 82.8 percent and 83.7 percent respectively.

The reason that Exxon was able to deliver more and lower priced gasoline than its rivals was simply its ability to obtain more plentiful and cheaper crude oil, said Dan Lundberg, publisher of the newsletter.

The December 1978 shutdown of nearly 6 million barrels a day of Iranian crude oil production rearranged the competitive position of many of the world's oil companies, the newsletter said. It noted that Exxon "as one of the four Aramco companies, is a principle purchaser of Saudi Arabian crude oil, which in 1979 was one of the cheapest in the wrold." The other Aramco partners -- Chevron Co., Mobil Oil Corp. and Texaco Inc. -- also fared better this past year, the newsletter stated.

The emergence of Exxon as the leading domestic gas market is the first time the company has been No. 1, although it has been among the top four since Lundberg first began his national share-of-the-market report in 1969.

A 10-year retrospective of the domestic market share for the top 11 oil firms also shows that Texaco, which led the pack seven years, pulled out of a number of markets in the early 1970s and dropped sharply beginning in 1975. By 1979, it had slipped out of the four-company cluster at the top, but the newsletter reported Texaco's four-year decline may have bottomed out.

In an interview, Mark Emond, editor of the Lundberg Letter, suggested that Exxon did not seek the No. 1 spot. "They find themselves in it because of their advantageous supply position," he said.

In previous years, Texaco was conscious of its dominance of the market and advertised that fact. Today, he said, preeminence might not be so advantageous.

"In this year, when people are supposed to be saving, why would a company publicly say that they are selling more gas than anyone in the nation?" he asked. "It's not in keeping with the conservation ethic."

Publisher Lundberg said he expects oil companies to be more and more aware of share-of-the-market reports, because if federal regulations governing pricing and allocations become stiffer, the oil companies' relative positions will become frozen.