They called it "Operation Jobs," this week-long effort by the Immigration and Naturalization Service to root out illegal aliens in what the INS said were attractive, relatively well-paying jobs that unemployed Americans might want.

So for the past week 400 INS agents waded through chicken blood and fish heads, explored steel mills, construction sites and pickle factories, and peered into restaurants, bars and nightclubs.

As the project was winding down, the results could best be described as mixed.

By week's end about 5,800 illegals, earning an average of $4.75 an hour, had been captured, and a substantial number of others were expected to be rounded up. The raids were targeted on Detroit, Denver, Chicago, Houston, Dallas, Newark, New York, San Francisco and Los Angeles.

In some parts of the country citizens and legal aliens were beginning to line up to apply for jobs, some paying up to $10 an hour, that the illegals had held.

But the INS has provoked lawsuits and protest from clergymen, civil libertarians and Hispanic groups charging that the rights of illegal aliens were being violated, and that the INS picked up legal aliens and even naturalized citizens in the raids. They also claimed that some illegals were taken away so quickly that children were left parentless.

In Boulder, Colo., a poultry worker fleeing a raid was killed when he ran in front of a gravel truck. The poultry farm said the victim, Jose Arnado Morales, was here legally. Robert Hester, an INS spokesman, said Morales was an illegal alien, and denied that agents were chasing him when he was hit. "Nobody even saw him," Hester said.

Duke Austin, a spokesman for the INS, conceded that some legal aliens might have been arrested as illegals because they did not have the green cards they are required to carry. He said detained aliens who have told the INS about children have been allowed to return.

Austin said it is too soon to judge the success of the experiment. That will depend, he said, how many of the jobs eventually are taken by Americans and other legal residents.

"We want to eliminate the magnet that draws illegals into this country," he said. "It will take some time to find out whether this had an impact."

Austin said the investigation had been targeted deliberately at jobs paying more than the minimum wage, rather than at occupations such as agriculture.

He said that a project like this could probably pick up tens of thousands of illegal aliens along the Mexican border. "If we wanted, we wouldn't be in Chicago, Denver and Detroit. We'd be down along the southern border."

One critic was Nickie Becker, office manager of the Petaluma Poultry Co. in Santa Rosa, Calif., who said she is having trouble finding Americans to replace aliens in jobs paying $5.25 an hour in her chicken-processing plant. She said in a telephone interview that when 30 INS agents raided the company last Monday, "You should have seen the goon squad. It looked like a Gestapo raid. I've never seen anything like it in my life."

Becker said the plant was shut down for two hours while the agents tracked through chicken blood, poking through refrigerators and trash barrels as employes fled in terror. She said 19 employes were handcuffed and taken away.

"One of them was from El Salvador and had papers showing he was legal. They dropped him three miles down the road and told him he could walk back," she said.

Becker said all the workers at Petaluma have shown some sort of identification, such as a Social Security card or official alien documentation. She said most of the workers are foreign because most Americans don't like that kind of work.

"They have to take the live chickens out of the truck and hang them upside down. Their throats are slit and they bleed all over the place before they go into the processing room where the guts are taken out. It's not a nice job. It's cold, it's damp. It's not the kind of job a nice, white, middle-class American wants to do," she said.

After the raid, Becker said she hired 27 Americans, but by week's end only about half a dozen remained. As they left, she said, many of the Americans told her, "I'd rather be on welfare."

Some of the jobs becoming available because of the raids are more attractive. Jim Aehl, a spokesman for the Claussen Pickle Co. outside Chicago, said that, after 43 illegals earning about $6.50 an hour were picked up on Monday, 250 people applied for their unadvertised jobs.

Austin said the INS has been bombarded with requests for job information. He said 1,000 people applied at the Price Feaster Brassworks near Los Angeles after 88 illegal aliens were picked up, and he listed other raids that created desirable jobs:

* Fifty illegals earning $7 to $9 per hour were arrested at the Robert Bosch Co. auto parts business near Chicago.

* The INS arrested 34 illegals earning $7.35 an hour at a Denver meat packer.

* Another 58 making $6 and more an hour were arrested at the Trinity Valley Steelworks in Fort Worth.

* Forty illegal workers making $7 and up were arrested at Bell Industries, a San Francisco computer assembler.

Although those jobs won't make much of a dent in the unemployment problem, Austin said Operation Jobs does show symbolically that illegal aliens are taking jobs Americans could fill.

Meanwhile, the protests pour in.

The American Civil Liberties Union has charged in a letter to President Reagan, Attorney General William French Smith and INS Commissioner Alan Nelson that the INS is "playing with people's rights to score a public relations victory" and is "scapegoating undocumented workers in an effort to shift the blame for the administration's dismal failure to cope with increasing unemployment."

The ACLU said the raids violated the civil liberties of large numbers of "foreign-looking" workers, adding that Hispanics appeared to be the "sole targets."

"This is discrimination pure and simple," said the letter, signed by ACLU executive director Ira Glasser and national legislative director John Shattuck.

Austin denied that charge. He said that on the average more than 95 percent of all illegal aliens apprehended by the INS are Mexican. Of those apprehended during Operation Jobs, he said, more than 17 percent were non-Mexicans.

Sen. Alan Cranston (D-Calif.) complained to the Justice Department, saying that the sweeps "upset communities and cause excessive hardship to all parties involved....There is evidence that the raids are sowing dangerous seeds of racial and ethnic conflict in California."

The raids sparked enormous protests in many target cities.

Rev. Pat Valdez, a Roman Catholic parish priest in Denver, said he's so outraged he's willing to harbor illegal aliens in his church and bar federal agents from entering.

In Los Angeles, attorneys for an immigrant-rights group won a federal court order Wednesday barring the imminent deportation of Mexicans who had been denied access to attorneys.

U.S. District Court Judge William Matthew Byrne broadened the ruling Thursday to require that people detained by the INS must be advised of their rights before they can be asked how they got into the country or before they sign a voluntary deportation form.

A federal judge in Chicago Thursday refused to grant an order forcing officials to let seized aliens meet immediately with lawyers. District Court Judge George N. Leighton said INS agents were doing their best in a difficult situation.

"It's common knowledge that when illegal aliens are arrested and detained they have a tendency not to give their real names...," the judge said, "and this sometimes causes delays."