Residents of the Florida Keys were ordered to evacuate today as Tropical Storm Rita approached hurricane strength on a path similar to that of Katrina, which devastated the Gulf Coast three weeks ago, and the mayor of New Orleans suspended a plan to start repopulating his flood-ravaged city.

With Rita forecast to become a Category 1 hurricane later today and to reach Category 2 strength Tuesday, tourists streamed out of the Keys and residents boarded up their homes and shops.

But a potentially greater threat looms later in the week, when Rita is projected to intensify over the warm waters of the Gulf, just as Katrina did late last month before slamming ashore about 60 miles southeast of New Orleans. On its current path, meteorologists said, Rita could hit the Texas coast by this weekend, bringing hurricane-force winds and torrential rains to an area that now houses thousands of evacuees from flooded New Orleans.

In view of the new storm, New Orleans Mayor C. Ray Nagin announced he was calling off his controversial plan to allow displaced residents to return, one neighborhood at a time, starting today. Nagin told a news conference in New Orleans that his "reentry program" has been going smoothly, but that now he was "encouraging everyone to leave" because of the threat from Rita.

"We have another hurricane that's approaching us," Nagin said. "So we've started the evacuation process as we speak."

Rita is "not an exact reprise" of Katrina, "but it's probably pretty close," said Frank Lepore, a spokesman for the National Hurricane Center in Miami. "It's got similar characteristics, except it's just a little lower in latitude. The issue is what happens when it gets out over the very warm waters of the central Gulf."

The storm was packing winds of 70 mph this afternoon and was projected to hit Key West about 6 p.m. Tuesday with winds around 105 mph, making it a Category 2 hurricane, Lepore said.

As Rita gathered strength, the Weather Service issued a hurricane warning for the southern tip of the Florida peninsula and for all of the Florida Keys. It said that at 5 p.m. EDT, Rita was centered about 345 miles east-southeast of Key West and was moving west-northwest at 14 mph.

The Weather Service said the Keys could be hit with storm surge flooding of six to nine feet above normal tide levels, "along with large and dangerous battering waves."

A mandatory evacuation order issued by Monroe County, Fla., covered about 80,000 people in the Keys, including 25,000 residents of Key West. Buses were sent to Key West High School to evacuate people who needed help to leave, and a military C-130 transport plane was dispatched to Key West Hospital to evacuate patients there. In addition, about 134,000 Miami-Dade County residents who live in coastal areas were under a voluntary evacuation order.

President Bush, after a meeting with homeland security officials to discuss Hurricane Katrina relief efforts, suggested that in view of Rita's approach, it would be a mistake for evacuees from New Orleans to return to that city in response to a plan by its mayor to start reopening neighborhoods.

Rita "now looks like it's going to head out into the Gulf, and could track Katrina, or it could head further to the west," Bush told reporters. "But, nevertheless, there is deep concern about this storm causing more flooding in New Orleans."

Mayor Nagin "has got this dream about having a city up and running, and we share that dream," Bush said. "But we also want to be realistic about some of the hurdles and obstacles that we all confront in repopulating New Orleans."

He said that if Rita brought heavy rains, "there is concern from the Army Corps of Engineers that the levees might break. And so, therefore, we're cautious about encouraging people to return at this moment of history."

According to Lepore of the National Hurricane Center, a five-day projection shows Rita reaching Category 3 strength in the middle of the Gulf, with sustained winds of about 115 mph and gusts up to 130 mph. Although its path is difficult to predict at this point, the latest projection has Rita heading toward Houston, a major oil industry center that is now also home to thousands of Katrina evacuees.

One concern is that Rita will hit "the general area where all these folks from New Orleans have been evacuated," Lepore said. "And there is enough hardship in that area as it is without throwing another hurricane at them."