Immigration and Naturalization Service Commissioner Alan C. Nelson said yesterday there will be no blanket policy allowing ineligible spouses of illegal immigrants who qualify for amnesty to remain in the United States.

Instead, Nelson told a House subcommittee during a hearing on the impact of the new immigration law that in cases in which one spouse qualifies for amnesty but the other does not, the INS could allow the ineligible spouse to remain in this country "if special humanitarian factors are present."

He did not elaborate on what the humanitarian reasons might be, other than to mention extreme illnesses or a handicap. Nelson also said that neither the spouse's relationship to the amnesty recipient nor his or her length of time in this country would be sufficient reason to allow that person to stay here.

Only illegal immigrants who arrived in this country before Jan. 1, 1982, and have lived here since then, qualify for amnesty. Therefore, thousands of immigrant families face the possibility of being separated because some members may qualify for amnesty while others do not, immigrant advocacy groups said.

At the hearing before the House subcommittee on immigration, refugees and international law, Nelson also repeated a previous announcement that minor children would be eligible for amnesty if both parents qualify for the one-year program that is part of the immigration law passed by Congress last year.

However, he added, minor children would not be exempt from deportation if only one parent qualifies for amnesty.

Immigrant rights groups and some members of Congress, who for months have been pressuring the INS to adopt a liberal family unity policy, were disappointed by Nelson's announcement.

"It's ridiculous and irrational policy," said Charles Kamasaki, a policy analyst with the National Council of La Raza, an immigrant rights group that has been pressing for a policy that would have allowed the ineligible family members to remain here and receive permission to work. "If they can do it for the kids, then they can do it for everyone else."

Sen. John H. Chafee (R-R.I.), who several weeks ago tried but failed to include an amendment to the State Department authorization bill that would grant special status to the ineligible family members, said, "This doesn't do the trick. It just doesn't solve the problem at all."

Bills are pending in the House and the Senate that would grant this special treatment to the relatives of amnesty recipients, but critics argue that the amnesty program will be over before any legislative action is taken.

INS officials said they do not know how many of the 850,000 illegal aliens who have applied for amnesty have minor children or spouses who do not qualify for amnesty, or both.

In explaining why the INS does not adopt a more liberal family unity policy on spouses, Nelson said there is no language in the immigration law itself giving the INS authority to grant special treatment to ineligible family members.

At one point during the hearing and in response to a suggestion by Sen. Romano Mazzoli (D-Ky.) that it would be more humanitarian to allow minor children to remain even if one spouse does not qualify for amnesty, Nelson, visibly angry, shot back: "Don't put us in the position of having to split up families. We are only following the law."