Gay marriage will soon be possible in nearly two-thirds of America's 50 states after a surprise decision by the Supreme Court not to intervene over key rulings of lower courts on the issue.

The decision means a further 11 states will now allow gay marriage, on top of the 19 where it is already permitted, taking the total number into a majority of states for the first time.

It came as nearly 200 Catholic bishops from around the world met in Rome to discuss, among other things, the Church's hostility to gay relationships. Conservative advocates for the family criticised calls at the Extraordinary Synod on the Family in Rome for the Catholic Church to welcome homosexuals.

The Supreme Court decision affects five states in which appeals courts had struck down bans against gay marriage: Virginia, Indiana, Wisconsin, Oklahoma and Utah, as well as six other states overseen by the same appeal courts: North Carolina, South Carolina, West Virginia, Colorado, Kansas and Wyoming.

Evan Wolfson, president of Freedom to Marry, told USA Today: "The court's letting stand these victories means that gay couples will soon share in the freedom to marry in 30 states, representing 60% of the American people. But we are one country, with one Constitution, and the court's delay in affirming the freedom to marry nationwide prolongs the patchwork of state-to-state discrimination and the harms and indignity that the denial of marriage still inflicts on too many couples in too many places."

Chad Griffin, president of the Human Rights Campaign, the gay rights group, said: "Any time same-sex couples are extended marriage equality is something to celebrate, and today is a joyous day for thousands of couples across America who will immediately feel the impact of today's Supreme Court action." But he added: "The complex and discriminatory patchwork of marriage laws that was prolonged today by the Supreme Court is unsustainable. The only acceptable solution is nationwide marriage equality."

The New York Times said in an editorial: "On Monday morning, the first day of the Supreme Court's new term, the most exhilarating news came not from anything the justices did, but from one thing they didn't do. Without explanation and against expectations, the court declined to hear any of the seven petitions asking them to reject a constitutional right to same-sex marriage. By choosing not to review those cases, the justices made it possible for same-sex couples in a majority of states to marry."

The Times continued: "It has been astonishing and moving to see the unprecedented speed with which the public and the judiciary have come around on the issue. A majority of Americans now support the right of same-sex couples to marry, compared with about a quarter in 1996. Among those under 30, support is at nearly 80 per cent."

In Rome, however, Voice of the Family, an umbrella group of Catholic laity from major pro-life and pro-family organisations, showed that resistance to gay equality in marriage remains strong on the religious right.

Referring to a testimony given to the Synod where a married couple, Ron and Mavis Pirola, called on churches to welcome homosexual couples, Maria Madise, Voice of the Family's coordinator, said: "The example given by the Pirolas – of ready acceptance of a son and his homosexual lover to a gathering where the grandchildren would welcome them into the family – gives a false lead to families and parishes. It is no example of love and mercy towards anyone.

"The unqualified welcome of homosexual couples into family and parish environments in fact damages everybody, by serving to normalise the disorder of homosexuality.

"It damages children by presenting homosexual relationships as models which may legitimately be chosen. It damages adults by making them complicit in tacit endorsements of the immoral and dangerous homosexual lifestyle. And it damages the homosexual couples themselves by failing to guide them with the truth in charity – that their relationship is gravely harmful for their moral and spiritual health."

She urged the bishops meeting at the Vatican not to change the traditional doctrine on homosexuality.

"The Church is clear that a truly pastoral approach will appreciate the need for homosexual persons to avoid the near occasions of sin," she said. "The Pirolas' presentation will lead to considerable confusion on the part of Catholics dealing with such difficult situations"

At Tuesday's daily Vatican press conference on the Synod, Cardinal Vincent Nichols, Archbishop of Westminster, said that the Synod responded to the Pirolas' testimony "very warmly, with applause".

John Smeaton, chief executive of the London-based Society for the Protection of Unborn Children, said: "Those Synod Fathers who, like Cardinal Nichols, welcomed the Pirolas' disturbing testimony show that they are totally out of touch with the real problems faced by families. The homosexual agenda is forcing its way into schools, universities, workplaces and sports clubs. The last thing families and parishes need is for Church leaders to tell them to welcome homosexual couples."