The Carter administration is considering creation of a large new class of U.S. residents who would be in a kind of legal and national limbo - not full citizens but not quite aliens either.

They would be called nondeportable aliens.

The idea is one alternative being sent to Carter by a Cabinet-level task force seeking a solution to the illegal aliens problem. It is now estimated there may be 6 million to 8 million such individuals in the country. The task force report is scheduled to go to the President in the next several days.

One proposal in it involves setting up two classes of illegal aliens, depending on how long they have been in this country, and giving different status to each.

Those who have been here longer that 10 years would be allowed to apply for so-called permanent residency, a status that would make them eligible to apply for full citizenship in five more years.

Those who entered the country less than 10 years ago but before Jan. 1 of this year would be made nonportable alines. They would be allowed to work but could not bring relatives to live with them, and if they went home even for visits, as many now do, they might not be allowed to return.

Creation of the new nondeportable alien category would solve some of the problems involved in giving full "amnesty" to all illegal aliens, task force experts say.

But it would create some civil liberties and other problems of its own.

"Since they could not look forward to attaining United States citizenship," the task force has warned of this group, "they would lack political rights and would probably never be fully integrated into our society."

"The mere creation of a large class of undeportable aliens . . . would cause resentment in the ethnic community," the task force added in one report on the subject six weeks ago.

Sources emphasized that the issue is so politically touchy that Carter will have to make many decisions himself, including the dates that would determine who gets permanent resident and who nondeportable alien status, if he chooses that option.

When he will make the decisions isn't clear. But Carter is already a month past his original timetable, and he told a congressional group Thursday he would have a message on the issue ready for Congress "Very soon."

A participant in the task force discussions thathave been going on fairly intensely for the past month - with Carter taking part at times - said two proposals everyone seems to favor are beefed-up policing of U.S. borders, including airline terminals, and stricter enforcement of existing minimum wage, overtime, safety, health, and fair labor standards laws.

Numerous studies done in recent years show that an overwhelming proportion of illegal aliens is paid less than minimum or prevailing wages for longer hours more strenuous working conditions and fewer, if any fringe benefits.

Most of the illegal aliens in the United States have come from Mexico. Their number has been growing in recent years. Organized labor claims they are taking jobs away from U.S. workers in a time of high unemployment. If found, illegals are deported.

The task force, including Labor Secretary Ray Marshall, Attorney General Griffin B. Bell, Health, Education and Welfare Secretary Joseph A. Califano Jr. and Deputy Secretary of State Warren G. Christopher, recommended in early, April 27 report to Carter that all illegal aliens who have been here five years or more be permitted to become legal residents.

They indicated in that report, which has not been officially made public, that creating a new, nondeportable category of aliens raised serious problems. But that report discussed the new caregory as an alternative of "full amnesty," and now a combination the two approaches is being proposed.

A task force aide who has been involved in the discussions said there are various advantages to the special nondeportable category.

"By having a fairly conservative amnesty you would avoid a number of problems," he said, "one being since you're not sure how many people want to take advantage of this, you may want to be conservative about how many people you're putting on the citizenship track."