Media playback is unsupported on your device Media caption Paul Ryan: Debt is the "overarching threat to our whole society"

US Congressman Paul Ryan has used a speech at a top Catholic university to defend remarks that his budget plan was inspired by Catholic teaching.

As a Catholic in office, Mr Ryan said, his work "conforms to the social doctrine as best I can make of it".

Faculty members and priests at Georgetown University had warned that Mr Ryan's spending blueprint would hurt society's most vulnerable.

Mr Ryan, a fiscal hawk, is a rising star in the Republican party.

His budget plan has been praised by presidential candidate Mitt Romney.

Misuse of teaching

Mr Ryan's speech hit back at the university faculty members and priests who signed the letter, as well as the policies of President Barack Obama.

"I suppose that there are some Catholics who for a long time thought they had a monopoly of sorts, not exactly on heaven, but on the social teaching of our Church," Mr Ryan said, adding: "There can be differences among faithful Catholics on this."

He also argued that a "preferential option for the poor", a tenet of Catholic teaching, means that people should not become "dependent on the government so they stay stuck at their station in life".

Catholic critics say Mr Ryan's budget plan hits the poor disproportionately, including cuts to the food stamps programme.

"We would be remiss in our duty to you and our students if we did not challenge your continuing misuse of Catholic teaching to defend a budget plan that decimates food programs for struggling families, radically weakens protections for the elderly and sick, and gives more tax breaks to the wealthiest few," said the letter by 90 faculty members and priests to the Wisconsin representative.

Analysis Paul Ryan talked about Subsidiarity, which emphasises the importance of local communities and institutions such as the family, the church and charities. It suggests they empower an individual and support the principle of the dignity of each person. But the Catholic theologians and bishops who have so vigorously condemned Mr Ryan's comments say Subsidiarity cannot be reduced to the notion that "Big Government is bad". It was developed to protect the individual, especially the vulnerable - the poor, the old and the sick. Of course, this leaves Catholic teaching open to interpretation and Mr Ryan isn't the first to use it to give philosophical substance to his political platform. On the Democratic side, Presidents Obama and Clinton have both used "the common good" as a rallying cry for a more progressive politics that embraces economic and social justice. Read more from Jane

The letter adds: "In short, your budget appears to reflect the values of your favorite philosopher, Ayn Rand, rather than the Gospel of Jesus Christ."

Mr Ryan's budget plan includes cuts to benefit programmes that would save $261bn over a decade, as well as large changes to government-sponsored health programmes Medicare and Medicaid and additional cuts to the defence department.

The plan also sets the highest tax rates at 25%, 10% lower than the current highest rate, and lowers the corporate income tax by half.

Mr Ryan, who unveiled his budget last month, recently said the Church doctrine of "subsidiarity" was reflected in his budget proposal.

"To me, the principle of subsidiarity, which is really federalism, meaning government closest to the people governs best," Mr Ryan said during an interview with the Christian Broadcasting Network.

But the letter from Georgetown University rejects this claim, saying: "Subsidiarity is not a free pass to dismantle government programs and abandon the poor to their own devices."

Correspondents say the letter offers a perspective from within the Catholic community that distances the Church from conservatives.

Catholic leaders recently criticised the Obama administration's decision to require employers to offer contraceptive services to their employees through their health coverage.

President Barack Obama attacked the Ryan budget proposal days after it was approved in the Republican-dominated House of Representatives last month.

He labelled the plan "social Darwinism" that would impose a "radical vision" on the country. He also noted in his remarks that Mr Romney had said the plan was "marvellous".