Washington (AFP) - President Joe Biden attempted a political high-wire act Tuesday by announcing a citizenship pathway for half a million immigrants married to US nationals, in a counterweight to his recent crackdown on illegal border crossers.

The Biden administration has been struggling to address immigration, a hugely divisive issue for many Americans ahead of November's presidential election.

"We can both secure the border and provide legal pathways to citizenship, but we have to acknowledge the patience of goodwill the American people is being tested by their fears at the border," Biden said at the White House.

The Democrat is seeking to be tougher on illegal migrants while contrasting himself with Donald Trump, whose attempt to win back the White House is centered on portraying the country as under assault by what he calls a migrant "invasion."

Biden's action to protect a whole class of immigrants was immediately condemned by Trump and other Republicans. However, it was hailed by immigration reform activists who had previously been dismayed by Biden's new border restrictions.

In his speech on the reforms, Biden said Trump was trying "to play on" Americans' fears."

The new rules will streamline the process for those who already qualify for permanent residence, by removing a requirement they leave the country as part of the application process.

The rules apply to those present in the country for at least 10 years and married to a US citizen before June 17, 2024 -- which the administration estimates to include around 500,000 people. In addition, some 50,000 stepchildren of US citizens are eligible.

Those approved will be granted work authorization and the right to stay in the United States for up to three years while they apply for the coveted green card. That would then allow them to apply later for full citizenship.

A senior administration official told reporters ahead of the announcement that the White House accepts much more is needed to fix the contentious and inefficient US immigration system.

However, "only Congress can deliver... comprehensive reform of our immigration and asylum laws."

Trump lashes out

Trump attacked Biden's policy in characteristic fashion, with lurid language and violent imagery.

"As innocent Americans are being beaten, raped, and murdered by Biden illegals, Crooked Joe Biden isn't taking action to stop this invasion or remove violent predators from our country," he said. "Instead, Biden is granting mass amnesty."

Far-right House member Marjorie Taylor Greene said Biden "wrote a vote-buying free citizenship executive order."

But groups campaigning for undocumented spouses of US citizens to get work permits celebrated.

"President Biden's action to extend work permits for long-term immigrant spouses is morally right, economically sound and politically smart," said Rebecca Shi, executive director of the American Business Immigration Coalition.

"The overwhelming majority of Americans support these humane and common-sense steps, and it will directly improve the lives of more than 10 million American citizens who have an undocumented family member," she said. "Today, those families, and the advocates fighting on their behalf, can breathe a huge sigh of relief."

Mexican President Andres Manuel Lopez Obrador welcomed the news as a "step forward."

Attempt to stem flow

The new protections for spouses of US citizens follow Biden's decision to impose dramatic new restrictions at the Mexico border.

A previous, bipartisan immigration package pushed by Biden in Congress would have introduced the strictest policies in decades, but it fell apart when Republicans walked away from the deal -- under pressure from Trump, whose campaign depends on portraying Biden as failing on the issue.

Biden then signed an executive order shutting down the border to asylum seekers after certain daily limits are hit -- a move that immediately drew criticism from the left and a legal challenge from rights groups.

The administration has defended its asylum order and characterized the congressional push as "the toughest and fairest set of reforms in decades."

Trump meanwhile has referred to immigrants as "poisoning the blood of the country" and promised mass deportations of those in the country illegally.

The Biden administration on Tuesday also simplified the process for migrants who came to the United States illegally as children -- known as Dreamers -- to get work visas if they've graduated college and have a "high-skilled job offer."