It took eight contentious years for Congress to pass the Immigration Reform and Control Act. It's been law for a year now, but the debate rages on.

One of its two principal authors, Sen. Alan K. Simpson (R-Wyo.), is pleased with his handiwork, but Rep. Edward R. Roybal (D-Calif.) says the bill is "the worst piece of legislation that we have passed in 25 years in Congress."

Roybal's chief objection to it is the reason that to date so few -- just over a million -- of the estimated 3.9 million who could step out of the shadows and into legal residency have applied. "They're afraid they will snitch on their families," Roybal said.

It takes a certain amount of raw courage for an undocumented worker to go to the Immigration and Naturalization Service. INS understood its ogre image with those who are now invited to regard it as an open-armed friend.

To provide a buffer between the nervous aliens and the service they associate with hunting, hounding and raids on the work place, INS set up several hundred Qualified Designated Entities, recruited from church, legal and community circles, to help the applicants through the maze of paper work required by the law. Even though the law provides stiff penalties for INS use of the confidential information provided by some luckless applicant who does not make it, the aliens are still in the grip of fear and mistrust.

They may remember the memorable words of INS western commissioner Harold Ezell, who, in sending his agents out to the border hunt, said, "If you catch 'em, you ought to clean 'em and fry 'em yourselves."

Even if the alien survives the first stages, he or she may fail to go on. The law makes only those who can prove they were in this country before Jan. 1, 1982, candidates for legalization. If a spouse or children arrived so much as a day later, they are disqualified and theoretically subject to deportation.

The INS insists that it is not sending women and children back home while father stays on. But Roybal says that his Los Angeles office has received questions from people who claim that the spouse has been ushered out of the country through Voluntary Departure. Roybal says they are "pressured" into leaving by the argument that she may take her place in the line for subsequent legal emigration without the black mark of deportation.

"We almost wrote into law the separation of families," Roybal said. "We criticize the Russians for this."

Roybal has an amendment in the continuing resolution that the House must pass before adjournment that forbids the use of INS funds for the deportation of spouses or minor children.

A much more generous effort by Sen. John H. Chafee (R-R.I.) failed last month. Chafee asked that legalization of one member be extended to others in the immediate family. Simpson forbade any tampering with his bill, fearing it might precipitate another eight-year war. He said it would be "unfair" to those who had been waiting patiently for legal admission. The INS notes that the bill, which makes no mention of families, grants "no statutory authority for derivative legalization."

Chafee countered that amnesty is a high national policy, undertaken for humanitarian and pragmatic reasons, which should not be foiled by restrictive regulations. His bill was tabled, 55 to 45.

Says Deborah Standiford of the Washington Lawyers Committee for Human Rights, "Here was Congress trying to do a fairly generous thing which it turned over to an agency that has traditionally seen its role as keeping people out of the country."

So far, final approval of the applications that came from 811,579 aliens and 211,078 seasonal agricultural workers, who were included for the benefit of farmers, has come to 151,602. An INS spokesman says that due to computer problems and procedural problems, it takes nearly six months to process a case.

The application period expires May 4. By that time, say advocates of the law, 2 million more will apply probably in a rush. But immigrant groups say that uncertainty and fear will keep them away -- unless, of course, INS comes out and says what it tells Congress privately: that it will not deport family members who don't have the right papers.

A move is on in Congress to extend the deadline. Other immigration legislation is in the works. Sen. Edward M. Kennedy (D-Mass.) has introduced a bill that would permit Europeans -- the Irish are flooding into Massachusetts these days to wait on tables, mind babies and do other chores -- to take places in the unused immigration quotas of other countries.

They are still banging on the Golden Door. The fight will never end over who deserves to get in or who deserves to stay.