For 21 days, Navajos hardly know whose clock to get up by. TUBA CITY'S TIME WARP

It's two weeks before the Navajo Indian Reservation and most of the country turn clocks back an hour, ending daylight saving time for this year. But in Tuba City - a typical, if somewhat large, reservation town of about 6,000 - you're behind the times if you haven't made the jump backward yet.

And half the town hasn't.

While Arizona has chosen to remain on mountain standard time year-round, the Navajo Nation, which occupies parts of three neighboring states, has officially opted for mountain daylight saving time from April to October ever since the 1960s.

But Tuba in October is a time-warped place where everyone is asking everyone else what time they're on. This is because it's the only community in the country - according to a US Department of Transportation official - that every fall functions with two time standards one hour apart: mountain daylight saving and mountain standard.

For just about everyone, the result is 21 days of confusion year after year. With the town's various stores, offices, and sole bank on different time, no one is left unaffected.

The source of confusion is the local public school district, which leaves daylight saving time on the first Monday of October for the sake of student safety.

Alice Weekley, superintendent of Tuba public schools, explains that the early return to standard time means that Navajo Indian children on the rural reservation can walk to their school bus stops and wait for their buses in the light rather than in the dark.

While fall days on the arid Arizona reservation remain warm, she says, mornings are chilly and bus drivers report that many of these students don't have warm clothes to wear. Changing time standards now, instead of at the end of the month like the rest of the country, provides an extra hour of warming sun.

One critic of the time distortion, Tuba lawyer Peter Osetek, says that all the district has to do is roll its schedule up an hour for three weeks rather than change time for the entire town.

``The easiest thing for the school to do if they have a problem is say, `OK, for the next three weeks school is starting at 9 o'clock and we will pick you up at 8 o'clock instead of 7 o'clock,''' he said. ``That way everything can function the way it normally would.''

Every year when the schools change their time standard early, an odd chain reaction occurs.

The schools are followed by the local Indian Health Service hospital because its workers' children conform to the public school time. And when the hospital changes, two nearby Bureau of Indian Affairs schools follow suit because their workers and students must use the health service.

And because these groups change early, the local movie theater, the post office and other businesses jump into the act.

But not all. Most federal workers and all Navajo tribal employees - the two largest employers on the reservation besides the school district - must remain on daylight saving time. For them the change means major inconveniences, with no court of appeal.

``It's just a big mess,'' Mr. Osetek says. ``It causes family problems. It causes problems at work because people are coming in late.... It's nuts.''

Nuts to some and illegal in just about anyplace else in the United States. Arbitrarily changing the time standard is a violation of the federal Uniform Time Act of 1966. But the government is not likely to take action here.

``We have the authority to go into district court and get an injunction to require uniform observance,'' says Joanne Petrie, an attorney with the Department of Transportation which enforces the law. But because the law addresses states and their political subdivisions, Indian reservations may be exempted, she says.

To Ms. Petrie's knowledge, Tuba City is the only town in the nation to use two time standards.