David Cameron will set out plans on Friday to create a "fairer, faster" adoption process - including moves to make it easier for white couples to adopt black children.
The Prime Minister is to say there is "no more urgent task" for the government and promised legislation to force councils to speed up the process.
As well as tackling the "absurd barriers" to mixed-race adoption, the changes will see more youngsters fostered pending approval of full adoption.
And town hall social workers will be legally obliged to turn to the existing national adoption register if they fail to place children locally within three months.
Full details of the shake-up are due to be published next week by Education Secretary Michael Gove - who last month criticised "misguided" efforts to insist on same-race matches.
Despite guidance issued last year, some local authorities were still putting their belief in finding "a perfect match" ahead of the children's interests, Gove, himself adopted, said. But although the Government said it would introduce the changes "as soon as possible", officials would give no commitment to the changes being made before 2015.
Cameron said: "This government is going to tear down the barriers that stop good, caring potential adoptive parents from giving a home to children who so desperately need one."
He said it was "shocking" that black children waited on average twice as long as their white counterparts to be adopted. "We will tackle the absurd barriers to mixed-race adoption which trap many non-white children in care. We will make sure that local authorities who let children down make faster use of the National Adoption Register.
"And we will remove obstacles to make sure potential adoptive parents can be foster carers too, so that it's no longer too hard for children to be placed with them while final decisions are made. Together, these are vital steps towards a system that is fairer, faster, and puts children and parents first."
The Adoption and Children Act 2002 says a child's welfare should always be the "paramount consideration" but requires "due consideration to the child's religious persuasion, racial origin and cultural and linguistic background".
Revised statutory guidance was issued last year in a bid to reduce delays faced by ethnic minority children but ministers believe it has failed to have a big enough impact. "Now we will go further and will bring forward primary legislation at the next available opportunity. We want to make it clearer that ethnic matching should not automatically be an overriding consideration in the matching process," a Number 10 spokeswoman said.
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