The temporary limit on non-EU arrivals is intended to prevent a "surge" in the numbers in the run-up to the introduction of a permanent maximum next April.
The immediate restrictions will mean that 24,100 workers from outside Europe can enter the country before April 2011 - a fall of 5% on last year.
Mrs May said the cap was just one of the measures being considered by the coalition Government in order to meet the Conservatives' election pledge to reduce net immigration to the "tens of thousands".
"Introducing this temporary limit is necessary to ensure that we don't get a rush of people trying to come through into the UK before that permanent limit is put in place next year," she told the BBC Radio 4 Today programme.
"What we have as an aim is indeed to bring immigration down from the hundreds of thousands that it became under Labour to the tens of thousands that it used to be. There are various ways in which we do that."
Mrs May rejected suggestions that there was little the Government could do to reduce overall numbers as the majority of immigrants came from the European Union.
She said that according to the most recent immigration figures, just over half - 52% - came from outside the EU.
She also dismissed suggestions that a cap would be economically damaging for the UK, making it more difficult for employers to recruit the highly-skilled staff they needed.
Some senior Tories are understood to have privately raised concerns about the impact on businesses, while the Liberal Democrats opposed the idea during the election.
However Mrs May said that other countries which operated annual limits on immigration had still been able to recruit the people they needed.
"I don't think that anybody would ever suggest that Australia or the United States or New Zealand, in operating an annual limit, weren't able to get into the country the skilled people that they need and that their economies were somehow suffering from that annual limit," she said.
Mrs May later said that the decision on where the annual cap should be set would take into account the social impact of immigration such as the pressure on schools, hospitals, council housing and other public services.
The Migration Advisory Committee has been tasked with determining what the limit should be - and also consider the impact on business and the economy - by the end of September..
Firms have been given 12 weeks to respond to a series of suggestions about how the cap system will operate in detail, including several aimed at easing the social impact.
Among them is the idea of forcing employers to provide private health insurance for foreign workers in an effort to reduce any "undue burden" on the NHS.
Those bringing in employees could also be told to show a commitment to training British workers by supporting schemes such as apprenticeships.
Rule changes could also oblige employers to make more effort to scour jobcentres for home-grown recruits, even in roles deemed to be among those facing a "national shortage".
"Migrants should only be brought in where every reasonable avenue to recruit a resident worker has been exhausted", the Home Office said.
Entrepreneurs are exempt from the cap but may be obliged in future to show their business ideas would create more than the presently required two jobs in the UK.
The Home Secretary said the consultation provided "various degrees of flexibility for business" over the operation of the cap which should enable them to meet concerns such as quarterly rather than annual applications for visas.
Ministers have indicated that they favour a "pool" system for highly skilled migrants but a first-come, first-served approach for the second tier.
Under the interim cap, the numbers of highly skilled workers allowed in will be kept at 2009 levels, meaning a maximum of 5,400 over the period until April.
They will have to meet a higher points test, however, "to ensure that those who do come are the brightest and the best", Mrs May said.
The number of skilled workers able to come in on the second tier of the visa system has been reduced by 1,300 to 18,700.
Exempt from the cap will be intra-company transfers, ministers of religion and elite sports people.
Mrs May said the proposed changes are "not just a tweak" but would not say how significant a part the Government hopes they will play in efforts to reduce numbers to the tens of thousands.
Action has already been take to strengthen requirements - such as language skills - for people coming to the UK for marriage and the question of students would also be considered, she said.
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