Cash-hungry members of the Organization of Petroleum Exporting Countries (OPEC) have begun cheating massively on their production quotas, and the resulting slide in world oil prices over the past month is starting to show at the gasoline pump.

OPEC members, who agreed to a 17.5 million-barrel-a-day production ceiling in March in an effort to dry up the oil glut that was even then depressing prices, have let production climb back to 19 million barrels a day, according to industry and government sources.

This increased availability of oil, while demand remains weak because of world recession, drove the spot-market price for Arab light crude to a summer low of $30.90 in trading yesterday. OPEC's target price for this crude is $34.

Partly as a result of this decline, the price of gasoline at service stations across America has dropped an average of 1.2 cents a gallon since July 4, and Exxon announced it was cutting the wholesale price of gasoline in some parts of the country by a penny a gallon yesterday.

But while government and industry analysts expect to see the price of crude continue to weaken in the days ahead--perhaps even dropping under $30 a barrel in September -- few expect it to fall to the low of $28 it hit during the spring glut, before OPEC set the new quotas.

Even fewer analysts expect the major oil companies to give back much of the 11 cent-a-gallon increase in the average price of gasoline that took place at service stations between mid-April and the end of June, as prices rebounded.

"OPEC clearly is in trouble and I think we will see a continued weakening of oil prices. But I still doubt that the OPEC pricing structure will collapse," John H. Lichtblau, president of the private Petroleum Industry Research Foundation said yesterday.

"There is not a single OPEC member that would not be worse off under a free market price, so you have to assume they will maintain a certain amount of discipline."

Dan Lundberg, publisher of the Lundberg Letter, which surveys prices at 17,000 service stations around the country, noted that from the spring of 1981 to April of this year gasoline prices fell 20 cents a gallon and said that had "put a tremendous pressure on the industry for an improved profit realization."

"I see those pressures working against major price cuts," Lundberg said. "Should there be a great increase in the production of crude and prices drop sharply on the world market, then prices for gasoline and heating oil would fall substantially. But I don't see that ahead."

While a number of OPEC members currently are producing more oil than permitted under the cartel's quota, the major violators at the moment appear to be Iran, Libya, Venezuela and the United Arab Emirates.

Iranian oil production has actually increased since last month's invasion of Iraq led to unsuccessful efforts by the Iraqi air force to bomb Iran's primary oil shipment center of Kharg Island.

"The Iranians are producing about 2.7 million barrels of oil a day and they're going great guns to increase production as fast as they can," a government analyst said. This number is more than double Iran's 1.2 million barrel-a-day OPEC quota.

Libya also has increased its oil production to about 1.3 million barrels a day -- almost double its 750,000 barrel quota -- and has been trying to spur sales through a variety of barter deals, equity deals and price concessions, industry sources said.

Venezuela, which announced at last month's emergency OPEC meeting that it was not going to observe its 1.5 million barrel quota if other nations planned to continue their flagrant cheating, has increased production in the last month to more than 1.8 million barrels a day, government sources said.

The United Arab Emirates, which has a quota of 1 million barrels a day, is producing between 1.1 and 1.2 million, according to the sources.

While the price of crude has been falling steadily as a result of the current surplus, the key factor in keeping it from plunging more precipitously has been the Saudi willingness to cut back production to about 6 million barrels a day to keep the market from becoming even more flooded.

"If the others keep increasing, I think Saudi Arabia will become unwilling to try to compensate for everyone else's increase," Lichtblau said. "But I think they are hoping OPEC can struggle along until the fourth quarter, when seasonal demand always increases. If world demand for OPEC oil rises to 21 or 22 million barrels a day in the fourth quarter, OPEC's situation could improve significantly."

But, noted one government analyst, even if demand picks up to this extent, OPEC at the moment has a 28 million-barrel-a-day production capacity.

"So even if demand goes up to 21 or 22 million barrels," the analyst said, "it's still going to be a pretty soft market. At least through 1983, I don't see any big increases."