Younger people take religion seriously "when they have the chance to learn about it," he said.
And Cardinal Keith O'Brien, leader of the Roman Catholic Church in Scotland, urged Christians to wear a cross to symbolise their beliefs.
It comes amid a growing debate about secularisation in British society.
Meanwhile, the Queen and Duke of Edinburgh have attended traditional Easter Sunday service at Windsor Castle.
During the service at Canterbury Cathedral, Dr Williams said it was the wrong time to "downgrade the status and professional excellence" of religious education in schools.
RE is not one of the subjects counting towards the English Baccalaureate, the standard for ranking schools brought in by the coalition government.
The English Baccalaureate ranks secondary schools in England according to the number of pupils who get good GCSEs in English, maths, science, another language and a humanities subject - either geography or history.
Supporters of religious education want to see it included in the humanities category.
By Robert PigottReligious affairs correspondent, BBC News
During his decade as leader of the Church of England, Dr Williams has repeatedly complained that Christianity is being marginalised in British public life.
Today he welcomed what he said was a reduction in active hostility towards religion, but issued a new warning.
It was that "serious and liberal-minded commentators" were embracing religion as a socially useful tool - for example for rethinking our "destructive economic habits" - but wanted to "pick out the best bits of religion without all the embarrassing beliefs that go with it".
The archbishop insisted that it was precisely those awkward beliefs - such as the actual resurrection of Jesus - that mattered in Christianity, and that without them it would cease to make sense.
His fear is that Christianity might survive the active hostility of atheists, only to succumb to a kind of asset stripping which reduced it to a set of well-meaning principles without really saying anything about God.
But the government says it is already a compulsory National Curriculum subject and the English Baccalaureate is to encourage more students to take up geography and history in addition to RE - not instead of it.
In his sermon, Dr Williams said: "There is plenty to suggest that younger people, while still statistically deeply unlikely to be churchgoers, don't have the hostility to faith that one might expect, but at least share some... sense that there is something here to take seriously - when they have a chance to learn about it.
"It is about the worst possible moment to downgrade the status and professional excellence of religious education in secondary schools."
Dr Williams said a hostility towards faith and religion in public life may have been tempered by a recent appreciation of the social value of religion.
But he said the ultimate test of Christianity was not whether it was beneficial to the human race, but whether the resurrection of Jesus Christ actually happened.
He said that for Christians a vision of reconciled love between people "is there only because God raised Jesus" and that the answer was not in scientific proof, but by the way believers lived with and in their faith.
The latest debate on faith in Britain was ignited after Conservative co-chairwoman Baroness Warsi warned that the nation was under threat from a rising tide of "militant secularisation".
The Muslim peer said in February that Europe needed to become "more confident and more comfortable in its Christianity".
Research carried out in the same month by a secularist foundation suggested three-quarters of people who describe themselves as Christian in Britain displayed only a low level of belief and practice of the religion.
The Ipsos Mori poll, for the Richard Dawkins Foundation for Reason and Science, was rubbished by the Church, with Reverend Giles Fraser, former Canon Chancellor of St Paul's, saying it was not fair to trump people's "self-identification" as Christians.
In his Easter Sunday sermon, Cardinal O'Brien told worshippers to "wear proudly a symbol of the cross of Christ" each day of their lives.
He also voiced concern at the growing "marginalisation" of religion.
Dr Williams also issued a call for peace in the Israeli-Palestinian conflict in the Middle East.
He said: "A visit to Yad Vashem, the Holocaust Museum in Jerusalem, will convince you why the state of Israel exists and must go on existing.
"A visit to any border checkpoint will convince you that the daily harassment and humiliation of Palestinians of all ages and backgrounds cannot be a justifiable or even sustainable price to pay for security."
He said: "We have to prod and nag and encourage the religious leadership in the Holy Land on all sides to speak as if they believed in a God who acts, not only a God who endorses their version of reality.
"We have to pray, to pray for wisdom and strength and endurance for all who are hungry for peace and justice, pray that people will go on looking for a truly shared future."
In March, Dr Williams announced he would step down as Archbishop of Canterbury - the head of the Church of England - in December, after 10 years in the role.
Rowan Williams has warned against "downgrading" religious education in secondary schools in his last Easter sermon as Archbishop of Canterbury.