WASHINGTON, Nov 9 (Reuters) - As the federal shutdown

continues, U.S. flights will be reduced to "a trickle" in the

run-up to the Thanksgiving holiday because of rising air traffic

control staffing shortages, Transportation Secretary Sean Duffy

said in remarks that aired on Sunday.

Major airlines were dealing with a third day of

government-mandated flight cuts after thousands of delays and

cancellations snarled traffic on Saturday. The shutdown, which

has reached a record 40 days, has led to shortages of air

traffic controllers who, like other federal employees, have not

been paid for weeks.

"It's only going to get worse... the two weeks before

Thanksgiving, you're going to see air travel be reduced to a

trickle," Duffy said on CNN's "State of the Union" program.

Millions of people usually travel in the run-up to

Thanksgiving, one of the most important U.S. holidays, which

this year falls on November 27.

"Many of them are not going to be able to get on an

airplane, because there are not going to be that many flights

that fly if this thing doesn't open back up," Duffy said.

DAILY FLIGHTS CUT

The Federal Aviation Administration instructed airlines to

cut 4% of daily flights starting on Friday at 40 major airports

because of air traffic control safety concerns. Reductions in

flights are mandated to reach 6% on Tuesday and then hit 10% by

November 14.

The FAA on Saturday said air traffic control staffing

shortages were impacting 42 airport towers and other centers and

delaying flights in at least 12 major U.S. cities, including

Atlanta, Newark, San Francisco, Chicago and New York.

A growing number of air traffic controllers have retired

since the federal shutdown started on October 1, Duffy said. The

FAA is 1,000 to 2,000 controllers short of full staffing, he

told CNN.

"I paid experienced controllers to stay on the job and not

retire," Duffy said. "I used to have about four controllers

retire a day before the shutdown, ...now up to 15 to 20 a day

are retiring."

Some 1,550 flights were canceled and 6,700 were delayed on

Saturday, up from 1,025 cancellations and 7,000 delayed flights

on Friday.

Airline officials privately said the number of delay

programs made it nearly impossible to schedule and plan many

flights and expressed alarm about how the system would function

if staffing issues worsen.

The cuts, which began on Friday morning, include about 700

flights from the four largest carriers: American Airlines ( AAL )

, Delta Air Lines ( DAL ), Southwest Airlines ( LUV ) and

United Airlines. The airlines are due to cancel about

the same number of flights on Sunday.

During the government shutdown, 13,000 air traffic

controllers and 50,000 security screeners have been forced to

work without pay.

Duffy had earlier said he could require 20% cuts in air

traffic if more controllers stop showing up for work.

Republican U.S. Senator Ted Cruz of Texas said he was told

by the FAA that since the shutdown started pilots have filed

more than 500 safety reports about mistakes made by air traffic

controllers because of fatigue.