The government will not fulfil its vow to reduce net migration to the tens of thousands by 2015, the Institute for Public Policy Research think tank says.
It predicts net migration - the difference between the number of people entering and leaving the UK - will fall to 180,000 in 2012, from its 2010 peak of 252,000.
But reductions cannot be sustained at the current pace, it says.
The government insists its policies are working and the target will be met.
In its report the IPPR estimates the number of migrants coming to the UK from outside the EU will fall by about 10% in 2012, because of new restrictions on foreign students and worsening economic conditions.
The left-leaning think tank also believes the number of people arriving from the EU could fall, and the number leaving rise, as the country's economic prospects decline relative to nations such as Poland, which has the largest immigrant group by nationality in the UK.
But it says this will not continue falling at the same rate in 2013 and 2014 as it is not feasible to make further reductions on the same scale in work or education migration.
It also says immigration flows from the EU could increase if the economy starts to recover in 2013.
The IPPR's associate director for UK migration, Matt Cavanagh, cautioned: "While policy changes will start to achieve significant reductions in immigration from outside the EU, this will not be enough to put the government on track to hit its target."
Mr Cavanagh said: "Ministers' only real hope of hitting their immigration target in 2015 is for a prolonged economic downturn to continue to make Britain less attractive as a destination and to induce more migrants already here to leave, something which we assume the government does not want to happen."
He acknowledged there was strong public support for reducing immigration but said there were "equally strong doubts" that the government could meet its target.
"By promising what it cannot deliver, the government - far from achieving its stated aim of taking the heat out of this emotive issue - will instead feed the public's sense of disillusionment," he added.
Mr Cavanagh said 2012 would be "a crucial year for coalition ministers" and warned immigration curbs brought in by the government could make it harder for businesses to employ overseas workers when the economy picked up.
The IPPR's report stresses that further restrictions on skilled migrants coming to the UK, such as a higher salary threshold for those on intra-company transfers, are unlikely to reduce overall numbers by more than 10,000.
It also predicts figures due to be published early this year will show the number of foreign prisoners returned to their home countries to have fallen during 2011.
The report has been dismissed by a rival think tank.
Alp Mehmet, the vice-chairman of Migrationwatch UK, said: "This is the usual carping from the Left.
"They know that the immigration system has been in an appalling mess and that the numbers must be reduced but they seem to have nothing constructive to propose.
"The plain fact is that the government are on course but have a very long way to go."
The pledge to reduce net migration to the tens of thousands was a key part of the Conservative Party manifesto for the general election in May 2010.
Chris Bryant, Labour's shadow Home Office minister, said the government had not set out workable policies to achieve its promise over the cut to net migration.
"The number of people coming to the UK for intra-company transfers is going up, student visitor visas are going up, while the number of foreign criminals being deported is going down," he said.
"There is a big gap between the rhetoric and the reality of the government's immigration policies - and it's this gap that risks further eroding trust and shows David Cameron is out of touch on this issue."
However, Immigration Minister Damian Green said: "IPPR's predicted reduction in net migration of 70,000 by the end of 2012 is consistent with hitting our target of reducing net migration to the tens of thousands by the end of this Parliament.
"We've limited non-EU workers coming to the UK, overhauled the student visa system and will shortly announce reforms of the family migration and settlement routes.
"The latest quarterly figures show that student visas issued are down 13% and the main work visas issued are down 18% compared to last year - an early sign that our policies are starting to take effect."