WHEN SOVIET Ambassador Anatoliy F. Dobrynin bounded into the crowded reception hall of a Cleveland Park residence last week a few moments after Secretary of State George P. Shultz had arrived, it was a moment full of symbolism and portent for the changing American and Soviet roles in the Middle East.

Dobrynin quickly closed in on Shultz and the beaming host of the evening, Iraq's deputy prime minister, Tariq Aziz. The team of official Iraqi photographers standing nearby blazed away with flashbulbs as the three men smiled and joked.

The photograph of Dobrynin seemingly blessing that moment of American diplomatic success is a windfall for the Baathist government in Baghdad as it seeks to explain at home its decision to resume full diplomatic ties with the United States after a 17-year rupture marked by bitterness and open opposition by Iraq to any kind of American role in the Middle East.

For the Ayatollah Khomeini's Iran, locked in a bloody four-year stalemate with Iraq, that image is also likely to reinforce the passion directed against the "two great Satans" for propping up the government in Baghdad.

To claim that the moment represented a setback for the Soviet Union would be to overstate the case. Iraq will continue to be heavily dependent on the Soviets for military supplies, and is likely to maintain its radical opposition to American policies on many Third World and Middle East issues.

But Baghdad's decision to resume ties with Washington now appears to challenge a fundamental Soviet assumption in the Middle East -- that American support for Israel and opposition to Palestinian nationalism would irreversibly alienate Arab nationalist governments, and give the Soviets an enduring strategic advantage in the region.

In one sense, Iraq's decision underscores a new reality in Arab politics that has been taking shape over the past four years. Both Israel and the Palestinians have ceased to be determinant issues for Arab-American relations, at least for the time being. For years the glue of Arab unity was vehement opposition to Israel combined with avowals of devotion to the Palestinian cause, but that combination has now been eclipsed by more pragmatic national concerns in Egypt, Jordan and Iraq.

Without stating that conclusion in such stark terms, Aziz echoed its premises in a reflective recounting of Iraq's decision to resume full relations with Washington.

He asserted there have always been "two keys to open the door of good relations: one, the American- Iraqi key, and the other the American-Arab key." Iraq's position was that "if you start with the first key, the door will be open. If you use the second key, it will open widely."

The time has now come, Aziz said, when the first key -- mutual recognition of the usefulness of a working relationship -- has been turned. "We dealt with this question in a natural way," he said. "The primary concern for any country has to be the national patriotic concern, and that was the case (in this instance)."

The second key -- in effect, the Palestinian cause -- would improve relations, but was no longer a prerequisite.

A willingness to separate national from Arab concerns represents a reversal of the feeling that swept through Iraq and the rest of the Arab world in June, 1967, when Israel destroyed three Arab armies and inflicted a humiliating defeat on the entire Arab world. Reacting in anger and refusing to accept that small Israel could have beaten them so easily, many Arab nations broke diplomatic relations with the United States and turned toward the Soviet Union for increased military supplies and diplomatic support. Virulent anti-Americanism swept the Arab world.

That tide has been ebbing since 1973, when the Egyptian and Syrian armies launched a surprise war against Israel and accepted American mediation to end it. Last week, following in the wake of Egypt, Syria, Algeria and others, Iraq became the last major Arab nation to restore the ties broken in 1967.

Moreover, it did so without getting the diminution of American support for Israel that Baghdad had repeatedly demanded throughout the 1970s as a condition for reversing its 1967 decision.

Iraq's continuing discussions with the United States over building a new oil pipeline that would help increase Iraq's war-damaged production by up to 3.2 million barrels a day over the next two years also suggests a new emphasis on economic factors in the Arab world that is likely to favor American interests over Soviet goals.

A number of diverse forces have combined to produce the search among key Arab nations for a new consensus that accords a lower priority to Israel and the Paestinians.

Among them are the world oil glut, the bloody stalemate in the Iran-Iraq war, the rise of religiously inspired terrorism out of the Khomeini revolution in Iran and two consequences of Israel's 1982 invasion of Lebanon: Israel's success in destroying the Palestine Liberation Organization's base in Lebanon, and conversely Israel's failure to pacify and occupy Southern Lebanon, where for the first time Arabs view themselves as waging a successful war of attrition against Israeli forces occupying Arab territory.

That the Arabs who are pushing the Israelis back to their border through guerrilla attacks are Lebanese Shiites, and not Palestinians, is widely remarked upon throughout the Arab world.

While Aziz was meeting with President Reagan and other senior administration officials here last week, the PLO was convening its national council in Jordan, where King Hussein forcefully urged the Palestinians to adopt his policy of trying to reach accommodation with Israel. Significantly, the Soviet Union did not send an observer delegation to the council, giving further evidence of an estrangement with Yasser Arafat's organization.

All of this does not add up to a significant turn toward "moderation" by former Arab radicals, nor to a necessarily enduring trend. The change is a circumstantial one that has to do with domestic realities and a regional imbalance that will be difficult to translate into any new regional peace initiatives. Iraq is concerned with balancing the even more radical axis of Syria, Libya and Iran and not with joining Egypt and Jordan in a search for peace with Israel.

The Reagan administration appears to recognize this new balance. Indeed, one of the changes that has made it possible is a quiet shift in American policy emphasis over the past six months that adroitly parallels and exploits the slippage in the Soviet position.

In the energy crisis atmosphere of the 1970s, American policymakers argued that the United States could not secure binding relationships with the Arab oil producers in the Persian Gulf without making significant headway in the Israeli-Palestinian conflict.

Throughout its first three years, the Reagan administration aggressively sought to disprove that notion in efforts ranging from "strategic consensus" to enforcing the May 17, 1983, peace agreement between Lebanon's Amin Gemayel and Israel. But after the disasterous loss of American life in Beirut and an aborted military confrontation that built Syria up as the Arab world's strongest power, the Reagan administration pulled back and began to respond to individual national concerns within the region.

This has proved to be an effective short-term policy. Coming as the Labor bloc reentered the government in Jerusalem, it has provided a welcome opportunity for reassessment. But the recent history of the Middle East suggests that the region does not tolerate an immobile American role for very long, and will find ways to scramble all assumptions yet again.