A diverse assembly of delegates met on Sunday to begin a process to debate and ratify a document that will define what type of government Afghans will live under.
Much of the debate is expected to centre on whether the Muslim country should adopt a presidential system as outlined by the draft constitution, with a leader enjoying strong powers.
The alternative is a parliamentary model with an influential assembly of representatives.
"Every government has made constitutions for themselves," said Abd al-Hafiz Mansur, an elected representative for Kabul.
"The present constitution is not for the future, it is for continuation of this government," he said in his speech for the post of chairman of the 500-strong Loya Jirga assembly.
Mansur, leader of a mujahidin group who favours a parliamentary system, came second with 154 votes.
But another mujahidin leader, Sebghat Allah Mujadadi, one of 50 delegates appointed by the president, won an outright victory with 252 votes.
Debate has already raged over the draft, with critics warning it focuses too much power in the hands of the president and risks widening the country's deep ethnic and factional divides.
King addresses delegates
The traditional Loya Jirga, attended by delegates from across the country, was opened earlier by former Afghan King Muhammad Zahir Shah, who enjoys the title "father of the nation".
Hamid Karzai favours a strong
Zahir Shah, who returned last year from three decades in exile, told delegates they "have full rights to make amendments and bring changes" to the draft.
President Hamid Karzai, a former mujahidin commander who gained the presidency with strong US backing, said the constitution would offer Afghans a stable future under strong presidential guidance.
"We are a post-conflict country, we need stability and a durable and sustainable peace," Karzai said, repeating his insistence that Afghanistan needed a presidential rather than parliamentary system.
Questions and concerns
Loya Jirga delegates, who include around 100 women, will from Monday start discussions to determine the delicate question of how large a role the national religion Islam will play in the new constitution.
US troops continue to fight Taliban
and al-Qaida forces outside Kabul
They will also debate the role of women, human rights and balance of power between the central government and provinces.
Over the past century Afghanistan has been an absolute monarchy, constitutional monarchy, republic, Soviet dictatorship and was ruled by the Islamist Taliban, but it has yet to experience democracy.
Powerful factions, international analysts and rights groups say the new constitution, which will set in motion democratic elections scheduled for June 2004, threatens to alienate ethnic groups and fails to distribute power evenly.
The current draft, which outlines a presidential system
under Islamic laws, does not explain how power should be shared between Kabul and the provinces.
Washington, however, has praised the document as a "milestone" in Afghanistan's reconstruction.