WASHINGTON — Congressional budget analysts, providing a positive economic assessment of proposed immigration law changes, said Tuesday that legislation to overhaul the nation’s immigration system would cut close to $1 trillion from the federal deficit over the next two decades and lead to more than 10 million new legal residents in the country.

A long-awaited analysis by the Congressional Budget Office found that the benefits of an increase in legal residents from immigration legislation currently being debated in the Senate — which includes a pathway to citizenship — would outweigh the costs. While the report was a clear victory for immigration proponents, it came just hours after Speaker John A. Boehner raised potential new obstacles for the bill, saying he would not bring any immigration measure to the floor unless it had the support of a majority of House Republicans.

The report estimates that in the first decade after the immigration bill is carried out, the net effect of adding millions of additional taxpayers would decrease the federal budget deficit by $197 billion. Over the next decade, the report found, the deficit reduction would be even greater — an estimated $700 billion, from 2024 to 2033. The deficit reduction figures for the first decade do not take into account $22 billion in the discretionary spending required to implement the bill, however, making the savings slightly lower.

The report was immediately seized on by backers of the bill as a significant boost to its prospects. Senator Charles E. Schumer, Democrat of New York, one of the bill’s authors, said the report “debunks the idea that immigration reform is anything other than a boon to our economy.”