Pol Pot's Khmer Rouge is believed to have been responsible for the deaths of 1.7 million people.
But after six years of negotiations and delays, not one former member of the organisation has been tried.
However, the UN five-member team says a trial in joint Cambodian and international courts could lead to Brother Number Two - Nuon Chea - being put on trial within 12 months.
"Both the United Nations and the Royal Government of Cambodia are starting from the assumption that the extraordinary chambers will be operational in 2004," team leader Karsten Herrel told a news conference.
The ultra-Maoist Khmer Rouge unleashed a four-year reign of terror on Cambodia in the 1970s, as their dream of turning the country into an agrarian utopia turned into the nightmare of the Killing Fields.
Many of the victims - men, women and children - were tortured and executed. Others died of starvation, disease or overwork in vast rural labour camps.
The Khmer Rouge's leader, Brother Number One, Pol Pot died in 1998.
During a week-long stay in the southeast Asian nation, Herrel said he would be discussing the details of the trial, from buildings to staffing to translation facilities and broadcasting.
The ultra-Maoist Khmer Rouge unleashed a four-year reign of terror on Cambodia in the 1970s
Another priority would be setting the scope of a budget for the trial, which will be paid for half by Cambodia and half by voluntary contributions from UN member states.
Speculation has centred on a total $40-million bill for a three-year trial, although Herrel said the funding aspect, particularly on the international side, remained uncertain.
Cambodia and the UN finally agreed a trial framework in March, although Phnom Penh has yet to ratify the deal - the final obstacle to it becoming law - due to a four-month post-election stalemate which has deadlocked parliament.
Despite several rounds of talks and the intervention of King Sihanouk, the three main political parties appear little closer to compromise.
Most analysts and diplomats fear the deadlock may last for several months yet, increasing the chances of the ageing former guerrilla leaders, most of whom are in their 70s, dying of old age before they ever see the inside of a courtroom.