HARLINGEN, Texas (AP) _ Federal officials prepared to check shrimp nets again Friday for ''trap doors'' to protect endangered sea turtles, but some defiant shrimpers threatened to ignore the law requiring them.

The rule requiring use of turtle excluder devices, or TEDs, was to go back into effect at 12:01 a.m. Friday after a six-week delay prompted by shrimpers' protests, including blockades of ship channels in Texas and Louisiana.

Some shrimpers, saying too much of their catch escapes with the turtles, promised to ignore the rule.

''I'll set my boat on fire before I pull a TED,'' said Gary Duncan, a shrimper from Boothville, La.

Coast Guard officials, however, did not anticipate problems.

''It's not a very popular regulation with shrimpers, and that's not a surprise to anyone, but they're aware that it's the law,'' said Lt. Pat Philbin, spokesman for the Coast Guard district stretching from the Texas- Mexico border to the Florida panhandle.

The Commerce Department on Tuesday reinstated the TEDs rule under a court order to protect the turtles in compliance with the Endangered Species Act.

Philbin said TEDs are one of many items the Coast Guard checks during daily random boardings. There will be no dedicated effort just to enforce TEDs, said Coast Guard Lt. Bob Carson.

Failure to use TEDs could result in a maximum $20,000 fine, but the Commerce Department will phase in its enforcement.

Vessels cited before Sept. 22 will be able to settle by purchasing and installing excluders before Oct. 15. From Sept. 22 to Oct. 15, shrimpers can have penalties reduced if they purchase and install TEDs within 15 days.

Environmental groups that sued to force the government to require TEDs hailed Commerce's decision as a victory for sea turtle conservation.

TEDs allow the turtles to escape drowning. The cage-like devices fit in the back section of a shrimp trawl. A grid across the middle allows shrimp to flow through but catches turtles. Waterflow through the device helps turtles escape via a trap door.

An estimated 11,000 sea turtles die each year in Gulf Coast shrimp nets, including the endangered Kemp's ridley, which is declining annually by an estimated 3 percent, according to turtle researcher James Ross.

Commerce Secretary Robert Mosbacher temporarily blocked the TEDs requirement after shrimpers along the Gulf Coast blockaded ports July 22-23 to protest excluder regulations. Mosbacher allowed shrimpers instead to limit their trawling times to 105 minutes, with the idea that most turtles wouldn't drown in that time.

John Knauss, Commerce undersecretary, said limiting trawling times does not work. ''The only way to ensure protection of these vanishing species is through the use of TEDs,'' he said.

Tee John Mialjevich, of Delcambre, La., president of Concerned Shrimpers of America, said the group will go to court to reverse the regulation but added, ''We're not going to have any more blockades.''

Shrimpers say they lose 10 percent to 30 percent of their shrimp through the TEDs. Commerce officials say side-by-side tests have shown losses of only 2 percent to 5 percent.

''It's like cutting a big hole in your net,'' said Sydney Herndon, chairman of Gulf King Shrimp Co. in Aransas Pass.

Herndon said his 48 boats would comply with the law, but that TEDs threatened to drive some shrimpers out of business.

He questioned how the United States can require TEDs while importing most of its shrimp from countries, including Mexico, where the devices are not used.

Jimmy Russell, president of the Brownsville-Port Isabel Shrimp Producers Association near the Mexican border, said he believes many shrimpers will refuse to use TEDs.

Y-09-07-89 1900EDT