In a joint letter to Iran's supreme leader Ayat Allah Ali Khamenei, Khatami and Parliament Speaker Mahdi Karubi warned that under these circumstances, there would be little motivation for people to vote.
The Guardian Council, a conservative watchdog, has disqualified more than 2400 pro-reform candidates from the elections.
Khatami and Karubi, the pro-reform speaker of the legislature, wrote to Khamenei to complain that only a few hundred candidates had been reinstated in reponse to his call for a second review of the blacklist, IRNA news agency said on Saturday.
But they vowed they would nonetheless "organise the elections on the planned date", in line with Khamenei's orders, the news agency added, citing an "informed source".
IRNA's source said the pro-reform government had submitted a list of 380 candidates it wanted reinstated, after Khamanei's intervention, but the Guardian Council had approved only 200 of them.
"Most of those reinstated are not leading figures," the source added.
Khatami and Karubi also complained the council's obduracy would "make the elections less competitive and reduce the people's interest in voting".
The reformists have accused the conservatives of mounting a "coup" to regain control of government and parliament and had called for the elections to be postponed, which Khamenei rejected.
About 120 MPs held a sit-in at
parliament and later resigned
About 120 MPs, who held a sit-in at parliament, have resigned, along with provincial governors and some ministers and deputy ministers - sparking threats of prosecution from hardliners.
For conservatives, the Guardian Council just did its Islamic, revolutionary and constitutitional duty when it disqualified more than 3000 out of 8000 prospective candidates for lack of respect for Islam and the constitution.
News of the banning on 11 January provoked what many see as the worst political crisis in the country since 1979.
In an attempt to resolve the struggle, Khamenei stepped in, resulting in the reinstatement of about 1300 candidates, but this has not ended the political conflict.
Khamenei called for a review after a meeting with Khatami and Karubi on Tuesday, but said the elections had to go ahead on time and warned that resignations aimed at impeding the polls were "against the law and prohibited by Islam".