Soviet pressures and radical Arab politics have frustrated conservation Moslem hopes of a united condemnation of the Red Army's invasion of Afghanistan at this weekends Islamic conference in Pakistan.

A major split on the issue has developed in Arab ranks, with Algeria, Libya, South Yemen, Syria and the Palestine Liberation Organization boycotting the Islamabad foreign minister's meeting. The boycott decision ended the surface unity among the both conservative and radical Arab states generated by shared oppostion to the March 26 Egyptian-Israli peace treaty.

Iraq, which usually has been identified with the radicals, remained a question mark, however, with no official indication whether it would attend the conference. The Baathist government in Baghdad has vociferously condemned the Soviet invasion of Afghanistan.

The differences among the Arab states over the Islamic conference appeared to undermine U.S. hopes for a united Islamic front as an effective counterweight to any expansion of Soviet influence in the strategic Persian Gulf area.

Strong pan-Islamic backing for Pakistan would also limit the political fallout for the United States in its support of the military dictatorship of President Mohammed Zia ul-Haq as a buffer between the Soviets and the world's oil lanes.

The fact that the opening of the conference and the start of Egyptian-Israeli diplomatic reltaions were both scheduled for Saturday was invoked by the so-called Steadfastness Front of radical Arabs in bypassing the Islamabad conference.

As major recipients of Soviet arms, the radicals are doubtless under major pressure to boycott the Islamic conference, but they also had their own reasons to go along with Moscow whatever their misgivings about the Kremlin's intervention in a fellow Moslem state.

For the radicals, the principle issue remains Israel. They oppose any division of attention from a concerted struggle against the U.S.-sponsored peace moves between Egypt and Israel, which they perceive to be the paramount threat facing the Arab states.

The radicals feel the Afghan crisis has deprived them of meaningful Soviet support in pressing their case. By the same token, with the Soviets now on the defensive over Afghanistan, the radicals feel powerless to pressure the United States for a Middle East settlement during a presidential election year.

Even such a normally uncompromising Arab leader as Libya's Col. Muammar Quaddafi is on record as admitting that little can be expected from Washington until the elections are over. Qaddafi claims that President Carter has promised "radical" changes in American Middle East policy in his second term.

[A high White House official has said, however, that Carter had made "no commitment, direct or implied about a radical change in American policy" in the Middle East. A White House source said Carter has expressed to Qaddafi "an interest in improved relationships."]

In that light, the radicals are boycotting the Islamabad Conference because they fear it will be an essentially American show, either run by the United States or pro-American Islamic countries such as Saudi Arabia. t

Indicative of the deepening rift among Arab countries were weekend articles attacking Saudi Arabia in the pro-Syrian Beirut newspaper Al Sharq.

Only 10 days after a Damascus visit by Prince Saud, the Saudi foreign minister, the newspaper played up reports of instability in the kingdom in the wake of the Grand Mosque seizure by religious zealots last month.

Mentioned were reports of massive capital flight from Saudi Arabia and of gun-running into its vast and basically uncontrollable territory.

To some extent such propanganda is considered normal for the Syrians, who suspect the Saudis may be behind the series of assassinations and bombings that Damascus has laid at the door of the fundamentalists Moslem Brotherhood.

But beyond such parochial considerations lies the basic difference in philosophy. The Saudis and fellow conservatives are worried first and foremost by the Soviet threat and to a lesser extent by the revolutionary attacks from Iran's Shiite Moslem revolutionaries.

Nonetheless, the Steadfastness Front radicals felt sufficiently embarrassed by the Soviet invasion of Afghanistan to avoid an outright refusal to attend the Islamabad meeting.

Their foreign ministers met last week in Damascus and effectively signaled their intentions by laying down two stiff conditions that were virtually certain not to be accepted. When that happened, the front members announced their boycott.

They had demanded that the conference be moved from Islamabad to Mecca, the site of the Islamic Conference's permanent secretariat, a suggestion not calculated to please the Saudis so soon after the Grand Mosque occupation there.

They also demanded that the date of the Islamabad conference be changed so as not to coincide with the exchange of Egyptian and Israeli ambassadors.

Farouk Kaddoumi, the PLO's defacto foreign minister, first said the PLO would attend the Islamabad proceedings in any case, but then fell into line with the other Steadfastness Front members.

The PLO, moreover, has further toughened its stand by calling for strikes Saturday throughout the Arab world to denounce the establishment of Egyptian-Israeli diplomatic relations.

Iraq, the Arab world's perennial odd man out, has tried to keep one foot in the radical camp and at the same time not alienate conservative Arab governments, thereby preserving its chances of playing arbiter between the two groups in the future.

Despite a 15-year treaty of friendship and cooperation signed with the Soviet Union in 1972, Iraqi President Saddam Hussein strongly condemned The Soviet invasion of Afghanistan.

"The foreign intervention in Afghanistan is a serious phenomenon that can be neither justified nor excused," he told a nationwide radio and television audience on Jan. 6.