* BP, Chevron, Marathon shut production in Gulf of Mexico
* Louisiana Offshore Oil Port stops tanker offloading
* Chevron, Anadarko evacuating workers, no output shut
* Exxon preparing for possible shutdowns (Adds Chevron output shut)
By Erwin Seba and Bruce Nichols
HOUSTON, Nov 8 U.S. oil companies were shutting production on Sunday as they evacuated workers from the Gulf of Mexico ahead of Hurricane Ida, which is forecast to roar across the offshore oil patch Monday before making landfall on Tuesday.
BP Plc (BP.L), one the Gulf's largest oil producers, said on Sunday some of its production was shut and nonessential workers were evacuated from Ida's forecast path. The company does not disclose amounts of shut production.
Chevron Corp (CVX.N) said it had also shut some production.
Marathon Oil Corp (MRO.N) had shut its Ewing Bank production platform after evacuating workers, a spokeswoman said on Sunday. The Ewing Bank platform can produce 11,700 barrels of oil and 10.5 million cubic feet of natural gas a day.
The Louisiana Offshore Oil Port, or LOOP, which takes in an average of 1 million barrels of foreign crude from cargo ships daily, stopped offloading tankers shortly after noon CST Sunday (1800 GMT) due to deteriorating sea conditions, according to a spokeswoman.
Anadarko Petroleum Corp (APC.N) said workers were being evacuated from platforms in the Gulf of Mexico on Sunday, but no oil production was shut in.
Exxon Mobil Corp (XOM.N) said it preparing for possible shutdowns ahead of heavy weather at offshore and onshore Gulf of Mexico locations including its Mobile Bay, Alabama, natural gas field.
Oil companies began lifting workers off of platforms in the eastern and central Gulf of Mexico on Saturday, said a helicopter company executive.
"We've had a very busy day," said Jim Shugart, executive vice president of marketing for ERA Helicopters of Lake Charles, Louisiana.
"We expect tomorrow to be pretty busy if the weather gives us a shot to complete what we're doing," Shugart said. "We started Saturday. They've been flying all day. Can't put a number on it. I would think like 30 or 40 helicopters."
Hurricane Ida was packing 100 mile-per-hour (161 kph) winds on Sunday, according to the U.S. National Hurricane Center, which rated it a Category 2 storm on the five-step Saffir-Simpson scale.
Ida is forecast to strike the U.S. Gulf Coast between Louisiana and Florida sometime Tuesday morning, the Hurricane Center said.
ConocoPhillips (COP.N) said operations in the Gulf of Mexico were continuing as normal on Sunday while the company monitors the storm's progress.
The LOOP continues to supply U.S. Gulf Coast refineries from tens of millions of barrels of oil stored onshore despite the halt in tanker offloading, said LOOP spokeswoman Barb Hestermann.
The LOOP also continues receiving via pipeline 500,000 barrels per day (bpd) in oil from the Mars and Thunder Horse production platforms in the Gulf, Hestermann said.
"We may not be offloading tankers Monday and Tuesday as well," she said.
The Gulf of Mexico accounts for 25 percent of U.S. oil production and about 15 percent of national natural gas output. according to the U.S. government.
(Editing Bernard Orr)