Once a hawk in OPEC councils, Iraq has turned into a dove about price increases and an innovator in devising ways to help underdeveloped nations pay their mounting oil bills.

This quiet change has accompanied Iraq's growing economic power since it moved -- after the Iranian revolution -- into Iran's traditional role as OPEC's number two exporting nation. Iraqi Oil Minister Mayed Adbul Karim underscored this in an interview today by saying that Iraq was expanding its capacity beyond its present 4 million barrels-a-day limit.

He said Iraq is currently producing from 3.4 million to 3.5 million barrels and could boost its production by "about 2 million barrels a day" once five small fields" start production, expected in 1983.

Also accompanying Iraq's new clout is a working partnership that Karim hinted his country has developed with its old rival Saudi Arabia, which is the leading member of the Organization of Petroleum Exporting Countries.

Saudi Arabia has been a moderating force on pricing among OPEC nations. Karim today seemed to suggest a solid understanding between Iraq and Saudi Arabia on oil questions and spoke of the "excellent relationship" between the "number one and number two producers" since late 1978.

At that time, strikes had closed down Iranian oil production even before supporters of Ayatollah Ruhollah Khomeini came to power in Tehran and decided to drastically cut back Iranian exports.

Karim criticized as "very dangerous, shortsighted, a two-edged sword" Iran's current high prices policy during a time of a sated oil market.

His country's pricing policy, he insisted, has been "rational and reasonable" ever since the ruling Baath Socialist Party seized power in 1968.

Explanations vary for Iraq's newfound moderation or its conversion to what Karim called a "gradual corrective price" policy.

Some observers insist that Iraq believes the current price levels create advantageous terms of trade for purchases of manufactured goods in the industrialized world and consequently should not be further increased. Others maintain that Iraq is coming of age and wants to demonstrate its best behavior, especially toward the Third World, before playing host to the 1982 nonaligned summit.

For a six-month experimental period starting last June 1, Iraq broke new ground by providing $254 million to some 20 underdeveloped countries to demonstrate President Saddam Hussein's new deal for the world's poorest nations.

His formula calls for OPEC members to earmark funds from oil price rises and developed nations to do likewise with cost increases in industrialized exports to the Third World.

Discussed first at an OPEC ministerial meeting last December, the formula is on the agenda of both the North-South dialogue between underdeveloped and industrialized nations and an OPEC summit conference scheduled here on Nov. 1.

In addition, Iraq, which the minister claims gave more aid proportionally to underdeveloped countries than any other OPEC member, provided a further $1.2 billion in grants and low-interest loans to four countries.

While saying that Iraq was expanding its current production capacity, Karim repeatedly stressed "we are no longer going to produce more than we need," and argued that industrialized countries should conserve oil and developed alternate energy sources.

Indeed, even at Iraq's present production level, the shortages of trained manpower are so acute and other bottlenecks are so serious that analysts are hard put to explain where almost half the present oil revenue -- estimated at more than $30 billion in 1980 -- are being spent.

The minister insisted that Iraq was spending every penny it earned from oil on development, however.

He confirmed that Iraq's prove reserves were second only to Saudi Arabia's, but refused to provide specific estimates.

Asked about Iraq's relationship with Saudi Arabia and that country's increasingly questioned ability to influence OPEC pricing policy by itself, the minister said, "it is a fact that no one country governs OPEC."

But he defended the Saudi thesis for the need of a "unified OPEC price" and claimed that "iranian capacity is less than 1 million barrels a day," for reasons he described as "technical, social and political."

Iraq has made no secret that it is helping Arabs resident in Iran's oil-rich Khuzestan Province in their drive for local autonomy. Iran has charged Iraq with responsibility in an increasing number of acts of sabotage against oil pipelines and other oil installation there.

Insisting that "Iran's prices are above what the market tolerates" $34.50 a barrel, the minister suggested that major American and Japanese companies were buying to replenish their depleted stockpiles.

Although the minister welcomed American companies willing to help Iraq with transfers of technology, he made clear that deep-seated political differences between Baghdad and Washington ruled out any significant breakthrough.

"We are very wary to start wide cooperation with the United States," he said, until Washington changes its Middle East policies.

The most important stumbling block -- which has prevented reestablishment of diplomatic relations broken in the 1967 Arab-Israel war -- is Iraq's uncompromising opposition to American support for Israel.