Oil and gasoline prices appear to be rising again.

Diamond Shamrock Corp., a large independent refiner, said yesterday that it will begin paying $2 a barrel more for domestic crude oil in most areas. In addition, the wholesale price of gasoline has increased an average of 1.61 cents a gallon in the past three weeks, with major oil companies as well as independents charging more.

"This may very well be the beginning of a round of price increases," said John Lichtblau, president of the Petroleum Industry Research Foundation. Lichtblau said the increases reflect the psychological success of moves by the Organization of Petroleum Exporting Countries to limit production and a need to replace depleted oil inventories rather than any surge in demand.

The full impact of wholesale gasoline price increases has been muted so far, according to Dan Lundberg, publisher of a newsletter that conducts nationwide surveys of gasoline marketing. While wholesale prices have jumped 1.61 cents a gallon, retail prices have only risen 0.66 cent a gallon.

According to Lundberg, a major factor has been price competition by Atlantic Richfield Co., which has kept its retail prices way below others' to offset possible losses of customers because of its decision to stop accepting credit cards.

Lundberg said that Arco prices have gone down as other prices have gone up. Arco's average price per gallon for regular unleaded gasoline at self-serve pumps is 3.77 cents a gallon below that average price for other majors and 1.92 cents below the average price charged by private brands, he said. That grade of gasoline accounts for 48 percent of volume and is what Lundberg called "a fighting grade."

Arco will not say how long it intends to keep prices that low, exerting downward pressure on other retailers' prices. "It is a long-standing Arco policy not to discuss changes in our pricing structure," a spokesman said yesterday.

"The credit card situation was an extraordinary one-time situation, and we did cover prices on that occasion," he said. "However, we can say that market factors and the rising cost of crude oil are exerting upward pressure on gasoline prices." Arco emphasized that it will continue to pass on a 2.8-cents-a-gallon saving to dealers to compensate for the elimination of credit cards, a decision announced by Arco early this year.

Diamond Shamrock said it has raised its purchase price by $2 to $32 a barrel for low-sulfur domestic crude from fields in the Texas Panhandle, West Texas, Oklahoma, Wyoming, Montana and North Dakota. The company had been paying the lower $30-a-barrel price for less than a month. Diamond Shamrock also raised the price it is paying for crude in some fields in Kansas and Colorado by $2 to $30 a barrel after a similar short-term drop in the price.

A spokesman for the company said that market conditions, including rising gasoline prices, supported the higher price. In addition, he said, the company's inventory has been depleted so it needs to buy more. Diamond Shamrock buys about 60,000 barrels of crude a day for a refinery in the Texas Panhandle.

Major refiners and independents have made dramatic reductions in inventories during the last quarter of 1981 and the first quarter of 1982. Industry analysts have predicted that prices would rise again as those inventories were diminished.

Lichtblau said that another factor in increasing domestic crude prices is that the average price for imported oil has been running several dollars higher than contract prices for domestic crude.