As the leaders of the world's nations avowing nonalignment assemble here for the opening Monday of their triennial summit conference, the movement is at another crossroads of ideological transition.

This time, in the seventh summit since the Nonaligned Movement was born in Belgrade out of the anticolonialist national liberation struggles of Asia and Africa, formidably organized forces of moderation are attempting not only to arrest a frequently contentious drift in the movement, but also to restore credibility that was blighted at the Havana summit conference in 1979.

As the chairmanship of the 101-member movement passes from Cuba to India, the more aggressively nonaligned nations are hoping to eradicate all traces of the notion floated in Havana that the Soviet Union was a "natural ally" of the movement. They seek to focus the week-long deliberations instead on broad political and economic issues upon which the summit's mainstream can agree with a minimum of rancor.

Draft summit declarations being circulated among the 70 heads of government and other nonaligned leaders concentrate heavily on nuclear disarmament, a restructuring of the international economic order and other areas of potential agreement, while studiously avoiding or toning down contentious issues that have marred previous conferences.

The preparatory meetings held here last week by foreign ministers have demonstrated the effectiveness of India's intensive presummit diplomatic effort to head off deadlocks on controversial issues and steer the conference toward relatively smooth agreement.

Even though the evenly divided ministers argued heatedly in three days of marathon debate over the recurring issue of which rival Cambodian delegation to seat--the Hanoi-backed government of Heng Samrin or the anti-Vietnamese exile coalition headed by Prince Norodom Sihanouk--the conference has been able to reach a "consensus" for leaving the seat vacant and thereby avoid a fractious showdown when the heads of government convene.

Although nearly half the ministers favored inviting Sihanouk, enough favored keeping the seat open to form a consensus under the movement's somehwat flexible definition of the term. India, the only noncommunist Asian country to recognize the Heng Samrin government, had favored leaving the Cambodian seat vacant.

Despite the polemics over Cambodia and the first tentative gusts of what--judging from past nonaligned meetings--will grow into a windstorm of anti-imperialist rhetoric, the tone of this conference is emerging with a distinct tilt toward restraint and centrism in the substantive decisions.

The draft declarations, prepared by India after consultations in 40 nonaligned capitals, mentions the United States by name only twice, once in urging a "constructive" U.S. position on negotiated solutions to conflicts in Central America and again in a brief reference to the Panama Canal, demanding respect for neutrality.

Puerto Rico's political status, a frequent vehicle for anti-American polemics in nonaligned declarations, is dismissed in the draft in one sentence that merely supports the right to self-determination.

The draft's section on the Middle East views with "grave concern and disappointment" the military and economic support given to Israel, but it does not identify the source or even mention the United States when discussing "strategic arrangements" in the Middle East that are said to encourage Israel's "hostile and expansionist policy."

Obviously pleased with the tone of the draft declarations, a U.S. diplomat here said: "It's a lot milder than previous declarations. We hope it will reduce the amount of controversy and build up the center view."

The two major thrusts of the summit, judging from the draft declarations and assessments by participants who arrived ahead of the leaders, will be global economics and arms proliferation by the superpowers.

The economic draft calls for the convening of a world conclave on the pattern of the post-World War II Bretton Woods conference that led to the creation of the World Bank and International Monetary Fund. The proposed conference would have the goal of restructuring those agencies to give developing countries a greater decision-making role.

The draft calls for the collective renegotiation of the developing countries' debt, expansion of World Bank lending, increase of IMF quotas and greater market access in industrial countries for exports from developing nations.

Although the proposed new economic order scathingly accuses developed countries of obstructing plans designed to help developing countries out of their economic binds, conference leaders have adopted a conciliatory tone seemingly aimed at ending the stalemate in the North-South dialogue.

Summit officials said the world economic conference would be held within the framework of the United Nations and that cooperation instead of confrontation would be sought.

"We cannot change institutions overnight," said Farouk Sobhan of Bangladesh, chairman of the Group of 77, a group representing 119 developing countries on trade and aid matters. "We have to do this gradually with a sense of purpose and pragmatism. We do not desire to work outside the IMF system. We desire reforms in the system to make it more equitable and responsive to our needs."

He said the summit would also seek to convene a meeting similar to the Cancun conference in Mexico to reestablish a North-South dialogue on world economic problems.

Also high on the economic agenda is increased cooperation between developing nations in trade, technology, energy development and other areas discussed two years ago in the New Delhi consultations, although such a dialogue could get bogged down in differences between oil exporting nations and non-OPEC members.

The economic issues are expected to get particular attention in this summit because in Havana they were dealt with in a desultory fashion only in the sixth day of the summit because of time-consuming political disputes.

The special attention given to the world economy, coupled with the expected emphasis on a proposed freeze on nuclear arms development by the superpowers, could serve to deflect summit debate away from some of the thorny issues that touch close to home among nonaligned member states.

Two nonaligned countries--Afghanistan and Cambodia--are presently occupied by foreign armies, and two others--Iraq and Iran--are at war with each other.

The incongruity of Afghanistan's occupation by troops of the nonaligned movement's professed "natural ally" has not been lost on the delegates, but apart from reaffirming U.N. calls for a comprehensive settlement of the issue, as nonaligned foreign ministers did here in 1981, the summit is not likely to dwell on the issue.

Similarly, there are no specific new proposals for reaching a settlement in the Iranian-Iraqi war, and the conference's planners have placed several neutral delegations between the representatives of the two nations in the conference hall here, in a departure from the customary alphabetical seating.

Other perennial issues on the agenda will be the creation of a "zone of peace" in the Indian Ocean and efforts to put Diego Garcia under Mauritian sovereignty, although the U.S. base there is not mentioned in the draft; Israeli withdrawal from Lebanon, and condemnation of South Africa's hold on Namibia, with the rejection of the notion of Namibian independence being linked to withdrawal of Cuban forces from Angola.

Amid extraordinary security arrangements for the leaders and 3,000 supporting officials who will attend the conference, New Delhi has undergone a metamorphosis in the weeks preceding the summit.

As they did last fall for the Asian Games, police have rounded up virtually all of the city's beggars and shipped them to detention centers on the outskirts of the city or put them to work frenetically resurfacing streets, painting curbs, planting flowers and hanging banners along the routes to be taken by the dignitaries.

Public works crews working in the dark of night have been corraling the sacred cows that traditionally wander the streets of Delhi, trucking them somewhere out of view of the delegates.

Several thousand security troops have been deployed around the conference hall and delegates' hotels, augumented in some cases by gun-toting personal bodyguard contingents such as the 150 commandos flown here by Iraqi President Saddam Hussein, who was to have hosted the summit until the site was changed because of the war.

India and Iraq have been engaged in a continuing dispute over restrictions on the number of automatic weapons that could be brought to the summit by security men.

Iran, whose delegation is scheduled to be headed by President Hojatoleslam Ali Khamenei, also has sought to transport a large number of armed Revolutionary Guards to the summit.

India today expelled 11 of 14 members of an Iranian commando squad that flew to New Delhi unannounced to guard Iran's delegates, United Press International reported. The commandos, heavily armed and dressed in green uniforms and army boots, arrived unannounced in a Soviet-built TU130 aircraft that landed here after ignoring repeated requests from the control tower to identify itself and disclose its cargo.

The Indian government and Iranian Embassy officials argued for several hours about the fate of the plane and its passengers before the plane left, leaving behind three of the commandos who were given permission by India to remain.

Iranian activists in New Delhi, along with Afghan exile leaders, have been placed under house arrest for the duration of the summit.