By CASSANDRA VINOGRAD

Associated Press

LONDON - First came love, then came marriage. But what if - someday - it's a girl in Kate Middleton's baby carriage?

If she's the royal couple's eldest child, new rules could push the princess to a prime place in history: the first girl to accede to the throne and beat out any younger brothers.

The Commonwealth countries agreed Friday to change centuries-old rules of succession that put male heirs on the throne ahead of any older sisters, following nations such as Sweden, Belgium, the Netherlands and Norway that have scrapped male primogeniture.

The move is a baby step - the changes must still be approved by the legislatures of the 16 nations where she is head of state before they could take effect - but is seen as a triumph over outdated, sexist practices.

April's lavish wedding of Prince William and Middleton - now known as Catherine, Duchess of Cambridge - renewed a decades-long debate over succession.

Middleton has rarely spoken about her plans for married life, but she did tell a well-wisher in Canada this summer that she hopes to start a family. William has said the same.

Once her honeymoon was over, baby talk started, adding urgency to the dialogue, although officials insist that talk of a pregnancy is premature.

Historians think it's about time the rules of the monarchy caught up with the times.

"You shouldn't muck around too much with the constitution, but it's a good idea to change this at this time," said royal expert Hugo Vickers. "It's much better to have it sorted out before any babies come along."

The thorny issue of changing succession rules has been an on-and-off topic in Britain, but has never been resolved.

The review started before William married commoner Kate Middleton in April.

William is second in line to the throne after his father, Prince Charles, who is the queen's first-born child. Charles' sister Anne is lower in the line of succession than her younger brothers Andrew and Edward by virtue of their male gender.

Charles, in turn, had only sons, William and Prince Harry, so the issue of gender was never raised.

The new rules would only apply to future heirs and would have no impact on the current line to the throne.

In 2009, then Prime Minister Gordon Brown's government considered a bill that would end the custom of putting males ahead of females in the succession line, as well as lift a ban on British monarchs marrying Roman Catholics. The government did not have time to pursue it before Brown's left office.

The rule has excluded women from succeeding to the throne in the past. Queen Victoria's first child was a daughter - also called Victoria - but it was her younger brother who succeeded to the throne, as King Edward VII.

But Prince William and his wife have been credited with freshening up a staid monarchy, and new succession rules will bring the royals more in line with modern mores in the 21st century.

"In this day and age, why should a royal son be more important than a royal daughter?" said Joe Little, managing editor of Majesty magazine, following the announcement of the agreement reached Friday in Perth, Australia, at a meeting of Commonwealth nations.

The same goes for the decision there to lift a ban on monarchs marrying Roman Catholics - which critics say is blatant discrimination since royals have free rein to wed Jews, Muslims, Hindus or members of any other religion.

"Britain is no longer the religious country that it once was," Little said. "While not denigrating the importance of religion, it plays much less of a role now then it did 60 years ago."

Still, some Britons remain wary of a Catholic monarch, like 73-year-old Anna Marsh.

"The pope is responsible for some horrors," she pointed out while on a break from cycling in London.

But her biking buddy Jill Gregory, 71, said she was fine with the idea - and also fully in favor of giving first-born females an equal right to the throne.

"In terms of ability, I don't think women are any different than men," Gregory said, pointing to Elizabeth II and her mother as examples.

Elizabeth II succeeded her father, King George VI, because he had no sons. If she had had a brother, however much younger he was, he would have jumped above her in the line of succession.

Britain's Prime Minister David Cameron had pushed the changes regardless of the difficulties or complexities in effecting them as he prepared for the Commonwealth meeting.

"We need to get on and do it," he said, calling it a matter of equality.

Now that the changes are agreed, New Zealand will chair a working group of Commonwealth countries to discuss how to accomplish the reforms set out Friday.

The 16 nations will need to begin their own individual legislative processes. In the U.K., that means passing and amending several pieces of legislation.

It's not a simple process - the complexity of getting all of the countries to begin legislative processes is what has held up these changes for decades in Britain and kept the debate from gathering full steam in the past.

However long it takes, Londoner Patricia Wager, 71, said changing the rules would clear up something that in the modern world should not still be an issue.

"It's a good idea, and a long time coming," she said.

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Associated Press writer Danica Kirka contributed to this report.