The biblical name Jacob, the most popular choice for baby boys for the sixth straight year, also tops the first official ranking of names given to twins. Parents like to pair it with Joshua.

Even more durable is the name Emily, which for the ninth year in a row claims the top spot among newborn girls, according to the Social Security Administration's tally for 2004, released Friday.

What's the staying power of Jacob and Emily? Hard to say, according to experts, but it has something to do with appealing to multiple ethnic or religious groups and having no widespread negative cultural connotations.

Jacob, for example, is the name of the biblical figure who fathered the founders of the twelve tribes of Israel.

"Jacob is number one because it has a long tradition," said Cleveland Evans, associate professor at Bellevue University (search) in Nebraska and president of the American Name Society (search). "Old Testament names are popular with both Christians and Jews."

Emily, No. 1 on the girls' list since 1996, is harder to pin down. Meaning industrious or striving, the name has strong literary associations including authors Emily Dickinson and Emily Bronte.

"The images of Emily are such that you can think easily of a woman who is both beautiful and smart," Evans said.

Neither name has a negative association that could topple it, the way Jason became unpopular after the widely seen "Friday the 13th" movies featured a maniacal killer by that name, Evans said.

This year for the first time, the agency also compiled a list of most-popular twin names. On the coed list, the top-ranking feminine pairing is Hope and Faith, ranked fifth. Taylor and Tyler, who could be either sex, came in second after Jacob and Joshua.

New to the single-baby top 10 are Isabella and William, both rising from 11th on their respective lists in 2003. Anthony and Alexis each dropped out of the top 10.

Just in time for Mother's Day, the agency updates its most popular 1,000 names by tallying applications for Social Security cards for children born during the previous year.

Almost every state lists as its most popular name some moniker that appears on the national top 10. A notable exception is New Mexico, which lists Alyssa and Alexis first and third for girls.

And Jose was the most popular boys' name last year in Arizona and Texas, which border Mexico and are heavily Hispanic. Anthony edged out Jacob atop Nevada's list.

Number 1,000 on the national list for 2004: Fisher for boys, Johana for girls.

The agency lists separate entries for different name spellings.