PESHAWAR, Pakistan (AP) _ With six weeks to go before Soviet troops are to be out of Afghanistan, the chairman of the Pakistan-based Afghan resistance on Tuesday announced a last- minute effort to form a transitional government.

Sibghatullah Mojaddidi said a consultative council - with half its members drawn from guerrilla commanders fighting Soviet and Afghan government troops - would convene within two or three weeks. The council would draw up a transitional government.

Apart from the difficulty of selecting and convening the more than 400 members of such a council, the decision offers the resistance little time to maneuver.

The Soviet Union's first deputy foreign minister and ambassador to Kaubl, Yuli Vorontsov, planned to arrive in Islamabad, the Pakistani capital, on Wednesday and meet Mojaddidi by the end of the week. It will be the second session between the Kremlin's Afghan specialist and the rebels in attempts to find a political settlement to the Afghan war.

The first meeting, in the Saudi Arabian city of Taif last month, was the Kremlin's first official recognition of the Moslem guerrillas it has been fighting for more than nine years. It was a tacit acknowledgment that Moscow is exploring a non-communist alternative to Preisdent Najib, head of the embattled government in Kabul.

Vorontsov was in Tehran on Tuesday meeting Iranian-based leaders of Shiite Moslem Afghan guerrillas, who operate separately from the Sunni Moslem groups based in Peshawar.

The main guerrilla alliance consists of seven squabbling parties who operate out of Peshawar under the name of the Islamic Unity of Afghan Mujahedeen.

The group, generally called the alliance, rotates its chairmanship among the leaders of the seven groups every three months. Mojaddidi, who became chairman Jan. 1, is the leader of the Afghan National Liberation Front, one of the alliance's relatively moderate but least militarily effective groups.

The decision to convene a consultative council, or shura, was announced after a fractious three-day meeting of the alliance's 140-member executive council. The council, comprised of 20 representatives from each of the seven parties, failed to unanimously endorse the plan, alliance sources said.

Some executive council members also opposed more meetings with Vorontsov, the sources said on condition of anonymity.

Mojaddidi said the council was a temporary measure because the war in Afghanistan makes an election impossible. At least two of the seven guerrilla leaders have advocated the election of a national parliament instead of summoning a consultative council.

But Mojaddidi said the alliance's supreme council, consisting of the top leader of the seven Peshawar-based parties, approved the shura plan a week ago.

He told a news conference the shura would have 400 or 500 members, with an equal number to be nominated by each of the seven parties. After the news conference, however, he told reporters each party would name 60 delegates for a total of 420.

He said 50 percent of the delegates would be rebel commanders. The rest would include well-known intellectuals, tribal leaders and ''good Moslems.''

He rejected the participation of any officials of the current Soviet-style Kabul government.

Mojaddidi's formula appears to exclude the Iranian-based Shiite guerrilla groups, but he said the seven Peshawar-based parties were free to nominate people who did not belong to their own ranks.

Shiites comprise only about 17 percent of Afghanistan's population, but they make up about 40 percent of the Afghan refugees who have fled their country since 1978 when a communist government seized power through a coup and needed the Soviet Union's 1979 military intervention to survive.

Of the estimated 15 million Afghans, one-third now live outside Afghanistan - 3 million in Pakistan and 2 million in Iran.

Asked whether the former Afghan king, Zahir Shah, would be asked to participate in the shura, Mojaddidi said any of the Peshawar-based groups was free to invite anyone.

The new attempt to form an interim government will take place in Pakistan, Mojaddidi said. Asked where and how it would operate, he first predicted confidently that the Najib government would fall quickly after Feb. 15, when the Soviet Union is scheduled to withdraw its last remaining forces, estimated at about 50,000.

But in response to questions, he said that if the guerrillas were not in control of the capital, the interim government would operate in provinces they did control.