WASHINGTON - The hopes for citizenship of 1.8 million illegal immigrants who came to the United States as children hung in the balance Monday as Congress started up debate on sweeping new immigration legislation.

President Donald Trump has offered more than Democrats asked on citizenship for the so-called Dreamers, but only in exchange for tough cutbacks on overall immigration and funding for a massive wall on the Mexican border.

A group of conservative senators were to introduce a bill Monday that closely follows Trump's January proposals.

The Secure and Succeed Act offers a 10-12 year path to citizenship for the 1.8 million Dreamers.

But it will also end the popular "Green Card lottery", a 28-year-old program to diversify immigrant arrivals, and sharply limit family-based immigration.

In addition, it will allocate $25 billion for tougher immigration enforcement including the construction of a wall along the US-Mexico border that Trump promised during his 2016 election campaign.

"This is the only bill that has a chance of becoming law, and that's because it's the only bill that will truly solve the underlying problem," said Senator Tom Cotton, a lead sponsor of the bill.

"This bill is generous, humane, and responsible, and now we should send it to the president's desk," Cotton said in a statement.

A clock is ticking: nearly 700,000 of the Dreamers, those registered under the Deferred Action for Childhood Arrivals (DACA) program, could begin losing protections from expulsion early next month.

The program's March 5 expiration date is not set in concrete, however - a San Francisco judge's injunction has at least temporarily blocked removal of DACA protections ordered by Trump late last year.

The Cotton bill could meet stiff resistance.

Democrats and some Republicans have opposed Trump's hardline stance, especially on its restricting family-based immigration to spouses and children, and on massive funding for the border wall.

But by expanding that to all 1.8 million DACA-registered or DACA-eligible young immigrants, and attaching it to other reforms, Trump has put the Democrats in a corner.

They originally pushed only for a permanent solution for the 690,000 DACA registrants, in separate legislation.

But Trump is adamant that overall immigration cutbacks be part of any deal.

The president has blamed domestic terror attacks and violent crime on the beneficiaries of the visa lottery and family-based "chain migration."

"We need a 21st century MERIT-BASED immigration system. Chain migration and the visa lottery are outdated programs that hurt our economic and national security," he said on Twitter last week.