President Barack Obama's administration is considering sending a letter to Iran aimed at unfreezing US-Iranian relations and opening the way for face-to-face talks, the Guardian has learned.

The US state department has been working on drafts of the letter since Obama was elected on November 4. The letter would be in reply to a lengthy one of congratulations sent by the Iranian president, Mahmoud Ahmadinejad, on November 6.

Diplomats say Obama's letter would be a symbolic gesture to mark a change in tone from the hostile one adopted by the Bush administration, which portrayed Iran as part of an "axis of evil".

It would be intended to allay the suspicions of Iran's leaders and pave the way for President Obama to engage them directly, a break with past policy. State department officials have written at least three drafts of a letter that gives assurances that Washington does not want to overthrow the Islamic regime, but merely seek a change in its behaviour.

The letter would be addressed to the Iranian people and sent directly to Iran's supreme leader, Ayatollah Ali Khamenei, or released as an open letter.

One draft proposal suggests Iran should compare its relatively low standard of living with that of some of its more prosperous neighbours and contemplate the benefits of losing its pariah status in the West. Although the tone is conciliatory, it also calls on Iran to end what the US calls state sponsorship of terrorism.

The letter is being considered by the new secretary of state, Hillary Clinton, as part of a sweeping review of US policy on Iran. A decision on sending it is not expected until the review is complete.

In an interview on Monday with the al-Arabiya television network, Obama hinted at a more friendly approach towards Iran.

The Iranian president Mahmoud Ahmadinejad said today he was waiting patiently to see what the Obama administration comes up with. "We will listen to the statements closely, we will carefully study their actions and if there are real changes, we will welcome it," he said.

Ahmadinejad, who confirmed he will stand for election again in June, said it was unclear whether the Obama administration was intent on just a shift in tactics or was seeking fundamental change. He called on the US to apologise for its actions against Iran over the last 60 years, including US support for a 1953 coup that ousted the democratically-elected government and the US shooting down of an Iranian passenger plane in 1988.

US concern over Iran is mainly over its uranium enrichment programme, which Washington claims is intended to provide the country with a nuclear weapons capability. Diplomatic moves are given increased urgency by fears that Israel might take unilateral action to bomb Iranian nuclear facilities.

The state department refused to comment today on options under review.

But diplomatic sources said lots of options were under review about how to signal to the Iranians that there is a change in attitude in Washington and that Obama is looking for direct talks.

One of the chief Iranian concerns revolves around suspicion that the US is engaged in covert actions aimed at regime change, including support for separatist groups in areas like Kurdestan, Sistan-Baluchestan and Khuzestan. The state department has repeatedly denied there is any US support for such groups.

The Bush administration, in its dying days, was planning to open a US interests section in Tehran, one step down from an embassy. The former secretary of state, Condoleezza Rice, said it never happened because attention was diverted by the Russian invasion of Georgia. Others say that right-wingers in the Bush administration mounted a rearguard action to block it.

The idea has resurfaced but if there are direct talks with Iran, it may be decided that a diplomatic presence would obviate the need for a diplomatic mission in Tehran, at least in the short term.

While Obama is taking the lead on Iran policy, the administration will shortly announce that Dennis Ross will become a special envoy to Iran, following the appointments last week of George Mitchell, the veteran US mediator, as special envoy to the Middle East and Richard Holbrooke, who helped broker the Bosnia peace agreement, as special envoy to Pakistan and Afghanistan.

Ross, who served in the Clinton administration in a leading role in the Middle East peace talks, will be responsible on a day to day basis in implementing Iran policy.

In a graphic sign of Iranian mistrust, the hardline newspaper Kayhan, which is considered close to the supreme leader, Ayatollah Ali Khamenei, has denounced Ross as a "Zionist lobbyist".

Saeed Leylaz, a Tehran-based analyst, said a US letter would have to be accompanied by security guarantees and an agreement to drop economic sanctions. "If they send such a letter it will be a very significant step towards better ties but they should be careful in not thinking Tehran will respond immediately," he said. "There will be disputes inside the system about such a letter. There are lot of radicals who don't want to see ordinary relations between Tehran and Washington. To convince Iran, they should send a very clear message that they are not going to try and destroy the regime."