So you'd like to learn Arabic. Got a decade or so?

Early last fall, FBI Director Robert Mueller made a public plea for Arabic, Farsi, and Pashto translators. Many Americans, eager to do their part in the war against terrorism, scurried to sign up for language classes. With more than 20,000 applicants to date for roughly 200 positions, the FBI is planning to satisfy its need for translators soon.

But all those now stuck in Introductory Arabic - with the daunting task of learning to decipher what to the untrained eye is nothing more than squiggles - should prepare themselves for a long haul. Mastering another language is never easy, but for English speakers, Arabic presents an even greater challenge.

For most, the biggest hurdle is the difference between the written, or classical, Arabic and the spoken dialects - a characteristic linguists refer to as diglossia.

The written Arabic is common to all Arab nations and is the language of the Koran - partly the mixing of a Meccan dialect with a poetic vernacular. It became fixed in the late 8th century, and has been more or less conserved since then. "I can't think of another language which has not changed appreciably in 1,400 years," says Wheeler Thackston, a Near Eastern languages professor at Harvard University.

Arabs themselves know this Arabic only through textbook education. It resembles what they grow up speaking at home as much as Latin resembles English, Professor Thackston says. They use it mostly to write and in more formal situations. It's the language of politicians and journalists, for example.

On the other hand, the spoken dialects - though they share characteristics with the written standard - vary by region, nation, and often, even by village. And they're constantly evolving.

As if that's not complicated enough, most Arabs, depending on the extent of their education and the circumstances of a given moment, will mix and match their own dialect with this literary Arabic. Osama bin Laden spoke such a version of Arabic in his widely broadcast tapes. That means any translator hoping for a steady paycheck needs to know both the written standard as well as at least one dialect. Linguists say a minimum of three years is needed for mastery of the written language alone.

Most US language classes, however, teach only the written Arabic, also known as Fusha. That's partly for practical reasons: On what basis does an instructor select from more than a dozen different dialects, each potentially fraught with political sensitivities?

The trend is for teachers to weave in small amounts of dialect, especially Egyptian, which, thanks to a burgeoning film industry, is fairly recognizable throughout the Middle East.

But Thackston, who teaches the only course in Levantine Arabic in the US (and one of only a handful of dialect courses), says many teachers unwiselyobscure the vast difference between the written standard and the dialects. Only many credit- hours and tuition dollars later do some students realize their knowledge goes only so far on the streets of, say, Morocco.

Most students, therefore, tend to get their dialect instruction abroad. The government is appropriating more money for programs like the Center for Arabic Study Abroad (CASA), which places American students in Middle Eastern countries for complete linguistic immersion. And Dr. Mahmoud Al-Batal, the director of CASA, expects interest in such programs to rise in the near future. But for now, he says, applications have tapered off.

In addition to diglossia, linguists also point out that Arabic has a penchant for synonyms and a cultural standard that encourages the use of obscure words, something that can stump novice speakers. "Arabic has a tendency to flaunt its rich vocabulary," says William Granara, professor of Arabic at Harvard.

Others, like Prof. Taoufik Ben-Amor at Columbia University, resist this characterization as an unnecessary mystification of the languagethat deters potential students.

Still, consensus reigns that, in any language, a good translator must have cultural knowledge of the region. This is especially the case for interpreting religious words or phrases in Arabic. For example, "God willing" is a phrase most Arabs unconsciously utter several times a day, regardless of religious beliefs.

r E-mail: farahs@csps.com.