A victory celebration in the streets of Baghdad last week to mark Iraq's apparent success in staving off the latest Iranian "human wave" attack across its border was revealed to be premature when another powerful explosion hit the Iraqi capital, exploding amid the revelers.

Iran later claimed that the blast was caused by a surface-to-surface missile it had fired from more than 100 miles away, although there was also speculation that it could have been sabotage.

The next day in Tehran, a radio address by Iran's spiritual leader, Ayatollah Ruhollah Khomeini, was abruptly cut off because of an Iraqi air raid.

In his speech, Khomeini had been talking about education and "piety." He had not mentioned the loss of thousands of irregular Iranian troops in the fierce ground battles in Iraq's Hawizah marshes or the decision of Iraqi President Saddam Hussein to raise the stakes in the long war by bombing Iranian cities.

The evidence is that Iraq goaded Iran into the latest ground offensive and that Iraq started to take advantage of its overwhelmingly superior air power. The muscle-flexing was as much geared at redirecting international attention to the 4 1/2-year-old Persian Gulf war, diplomats and analysts here surmised, as it was a new initiative to force Iran into negotiations to end the fighting.

But four explosions in Baghdad in six days shattered the illusion that the Iraqi capital was beyond the reach of the war, although Iran's claim of having new missiles remained suspect.

There was a moment of panic early last week in Washington that Iraq's strategy may have backfired. The thousands of lightly armed but religiously zealous Iranian Revolutionary Guards, in dinghies and primitive small boats, advanced across the marshes against Iraq's sleek, modern French- and Soviet-made tanks and helicopter gunships and appeared to have succeeded in their objective of seizing a portion of Iraq's main highway linking Baghdad with the oil fields and port of Basra, Iraq's second-largest city.

But meeting the Iranian troops on what amounted to a killing ground, the Iraqis put down the limited offensive, inflicting heavy casualties as they evidently resorted again to the use of chemical warfare, and scattering surviving Iranian irregulars back into the reed forests and vast lagoons of the marshes.

"In the end, if you get fanaticism against armor, armor is going to come out" on top, one U.S. analyst said afterward.

But if U.S. officials were quick in the aftermath to declare an Iraqi victory in the latest fighting, analysts here and Iraqi commanders on the scene were less sanguine about having broken the cycle of Iran's hit-and-collapse offensives that has forced Iraq to defend against possible attack up and down its more than 700-mile border with Iran and put any decisive end to the war out of sight.

"It's a war of attrition in a classic sense," military analyst Anthony Cordesman said.

Iraqi Maj. Gen. Sultan Hashim told foreign and Iraqi journalists touring the marshland battlefield littered with the bodies of Iranian soldiers that he doubted the latest fighting would be the "last such mass attack from those people," news services reported.

The faint hopes that this round of fighting and bombings might lead to negotiations for a settlement were based on the frantic shuttle diplomacy of the Iranians among their allies, Libya, Algeria and Syria, and at the United Nations to win support for a reimposition of the truce the United Nations brokered last June. In that accord, both sides agreed not to attack civilian targets or use chemical weapons.

That accord was shattered on March 4, when Iraq, apparently frustrated by the failure to make any progress at the United Nations on even the relatively minor issue of exchanging prisoners of war, bombed an unfinished nuclear plant at Bushehr on the gulf and a steel plant in Ahwaz in the Arab Khuzestan region of Iran.

After Iran retaliated by shelling Basra, Iraq raised the ante again by bombing more than a dozen Iranian cities and effectively shutting down commercial air traffic to Iran from outside the Middle East by threatening last week to shoot down passenger planes flying in or out of Tehran's Mehrabad Airport.

The Iranian envoy who met last week with U.N. Secretary General Javier Perez de Cuellar in New York reportedly suggested that the United Nations had the obligation of keeping it a "clean war," according to Arab diplomats who scoffed at the idea.

But Iraq, rejecting any further "piecemeal" approaches to the conflict, is insisting on a "comprehensive settlement" as its price for reining in its newly unleashed air force.

"We will continue to hit everywhere in Iran, at all times, until the leaders of Tehran crawl helplessly," one government broadcast in Baghdad threatened.

The day after his speech was interrupted, Khomeini was on the radio again in Tehran repeating his longstanding demand that Iraq's president be ousted if the war is to end, throwing cold water on speculation that forces around him favoring a settlement were gaining strength.

Secretary of State George P. Shultz, in an interview published Sunday in The Boston Globe, suggested that a speech by Khomeini on Thursday has "the possibility of saying that the Iranians can say they have done their duty because they've made a major effort." But Shultz added, "I don't want to be put down as concluding that's so. I just don't know."

Khomeini had said in his speech, according to The Associated Press: "Victory or defeat loses any meaning, because serving God and obeying His orders is all victory. . . . Even if we are defeated or not defeated . . . it makes no difference."

Iraq long has had command of the skies over Iran, which is believed here to be finding it increasingly difficult to get weapons and spare parts for its aircraft after alienating both the United States and the Soviet Union. Cordesman and other gulf war analysts calculate that Iran was probably down to 60 or 70 operational warplanes compared with at least 300 combat aircraft in the Iraqi Air Force, and that Iraq enjoys perhaps a 3-1 advantage in artillery and armor.

Iran's advantage seems, as before, to be in its population -- Iraq's is slightly more than 14 million compared with the more than 40 million in Iran -- and the Khomeini regime's far greater willingness to accept thousands of "martyrs" as casualties in repeated offensives that achieve no tactical purpose other than to keep the war going.

Iraq, far more sensitive to the effects of massive casualties on domestic opinion about the war, had been reluctant in the past to make wider use of its air power. Analysts here saw Iraq's escalation of the war as an expression of greater confidence and the new feeling that it was capable of turning back Khomeini's ground offensives and did not have to hold its Air Force in reserve to defend against them.

Iran's cities appeared to be lightly defended against air attack, but the analysts said Iraq seemed unable to disrupt operations at Iran's main oil facility at Kharg Island, surrounded by a fortress of air defenses and alternate mechanisms erected by the United States before the shah was overthrown.

Although Iraq's raids on the cities clearly caused alarm in foreign capitals, it remained unclear just what impact it was having on the Iranians. Foreigners who scrambled to get out of Tehran as Iraq's air blockade approached told reporters in Western Europe that after the first few days of raids, many residents of the Iranian capital emerged from shelters to go on rooftops and observe the play of warplanes and antiaircraft batteries.

Over the weekend, Iran warned it would retaliate by attacking Baghdad's airport with the missiles it claims now to have.

Iraq said Sunday that its warplanes had struck two oil tankers in the Persian Gulf near Kharg Island, The Associated Press reported. Shipping sources reported damage to the Maltese-registered tanker Eastern Star and possibly to the Italian tanker Volare as well as minor damage to the Kharg facility.

[The official Iranian news agency, IRNA reported that Iran launched a missile attack against Baghdad before dawn Monday in retaliation for an Iraqi attack on shipping in the Gulf, Reuter said. There were no immediate reports of casualties. Agence France-Presse added, quoting Iranian radio in Tehran, that Iraqi planes bombed the outskirts of Tehran, 45 minutes after the Iranian attack on Baghdad.]

Initially skeptical, U.S. officials thought at first that the explosions in Baghdad were caused by saboteurs -- and they still are convinced that the first, which destroyed the headquarters of the government-owned Rafidan Bank, was. But after viewing some of the damage in later explosions, they were willing to believe that at least some had been caused by missiles.

The speculation here and among western diplomats in the Middle East was that Iran may have acquired Soviet-made Scud B missiles from its main allies, Syria and Libya, but they were unable to explain how such weapons, which have a range of about 125 miles and an error range of about two-thirds of a mile, appear to have scored fairly accurate hits.

An Iranian diplomat contacted by the Christian Science Monitor in Paris said Iran had captured Iraqi Soviet-made missile launchers during an offensive in the spring of 1982 and it had taken almost three years for the military to find missiles on the international arms market that were compatible with them.

In a sermon in Tehran on Friday, Iran's parliamentary speaker, Hojatoleslam Ali Akbar Hashemi Rafsanjani, said, according to Iran's news agency: "These missiles, their numbers are so great that we shall make use of them to the end of the war. You should not ask where we obtained these missiles. If you wish, we will attach the tag 'Made in Iran' on future missiles."