Figures published by the Homeless Initiative suggest that there are 2,900 homeless adults in Dublin, Kildare and Wicklow at any one time, more than double the number estimated up to now.
The finding casts doubt on the accuracy of previous surveys of homelessness by local authorities throughout the State.
Voluntary agencies greeted the results by calling for a drive to house 9,000 homeless people in Dublin, Kildare and Wicklow.
The voluntary agencies - Dublin Simon Community, Failtiu Day Centre, Merchant's Quay Project, Threshold and Focus Ireland - called for a major expansion in social and public housing as well as a range of other measures to respond to the level of homeless revealed in the survey. The agencies had suspected that more people are homeless than was previously thought.
The measures the agencies called for include giving priority for housing to 3,000 homeless people a year for three years, and Government investment of £115 million in voluntary agencies over a five-year period. Mr Greg Maxwell of Dublin Simon Community said the finding that 2,900 people were homeless in the week of the survey means that 10,000 people could experience homelessness for periods in Dublin in any one year.
Previous official estimates suggested there were about 1,400 people homeless in Dublin and 2,500 in the whole State.
These figures have been widely criticised as too low. The Homeless Initiative, a project directed by Dublin Corporation, the Eastern Health Board and various voluntary and statutory bodies in the field, commissioned a survey by the Economic and Social Research Institute to arrive at an accurate figure for the EHB region.
The revelation that almost 3,000 people were homeless in the region in the week of the survey - almost all of them in Dublin - drew a strong reaction.
"The resources are available to deal with homelessness, but the political will and energy are absent from this Government to act," said Labour Party spokesman on the environment and local government Mr Eamon Gilmore.
The Lord Mayor of Dublin, Councillor Mary Freehill, said that "as a society, it is unacceptable that there should be that many individuals who have to face such a daily struggle".
The survey distinguishes between two groups of homeless people. One group of 1,550, mostly young women with 820 children, are on the local authorities' list of homeless people and are staying with friends or relatives - but on such an insecure basis that the housing authorities regard them as essentially homeless. The other, of 1,350 people, mostly older, single men, with 170 children, are users of services for homeless people. These services include hostels and food centres.
The Minister of State for Housing and Urban Renewal, Mr Robert Molloy, said at yesterday's launch of the report that the Government would announce a programme of additional measures to respond to homelessness following consideration of the report of an inter-departmental committee which is expected later this year.