The chairmen of the House and Senate immigration subcommittees yesterday introduced a major immigration reform bill that rejects much of what the Reagan administration requested last fall.

The bill would give permament resident status to millions of illegal aliens, set up stiff penalties for employers who knowingly hire illegal aliens and require a national form of identification to be presented by all Americans and aliens when they begin new jobs.

The administration indicated it felt it could work from the new bill as a basis for compromise, but whether Congress will pass complex immigration legislation in this election year was a question.

The Census Bureau estimates that there are between 3.5 million and 6 million illegal aliens in the country. Government figures indicate that an additonal 500,000 may enter each year.

The bill, introduced by Sen. Alan Simpson (R-Wyo.) and Rep. Romano L. Mazzoli (D-Ky.), would give immediate permanent resident status to illegal aliens who prove they have lived in the United States continuously since Jan. 1, 1978.

It would give temporary legal status to those who can prove they have been here since Jan. 1, 1980, and to Cubans and Haitians with special status who arrived in the 1980 boatlift. A person's temporary status could be upgraded to permanent status two years after the bill is enacted.

After receiving permanent status, aliens would be eligibile for citizenship in five years under the normal naturalization rules.

The administration proposal, however, would keep illegal aliens in the temporary status--unable to bring spouses and children to this country--for 10 years after the date they arrived here, a term many critics charged was too long to be realistic.

Other key differences between the Simpson-Mazzoli bill and the administration proposal:

* Simpson-Mazzoli does not include special powers that President Reagan had requested to deal with immigration emergencies, including the power to shut down roads, airports and even cities and harbors to head off approaching illegal immigrants.

* The Hill proposal omits a new guest worker program, especially popular in the West and Southwest, requested by Reagan. Instead, it would keep temporary workers under the strict control of the Labor Department but would streamline some of the paperwork.

* Reagan opposed a national identification system, but the bill directs him to devise a "universal employment authorization" system within three years.

Simpson said this could be an identity card or a data bank maintained by the government that an employer could check before hiring an applicant.

"It won't be an internal passport or a card you have to carry all the time . . . . It will not be a card which some jack-booted minion mashes your door down" for, Simpson said, referring to fears expressed by civil libertarians that such a system could be used by the government as a tool of repression.

The Hill measure provides stiffer penalties for employers than the administration asked: a $1,000 fine per illegal alien for the first violation; a $2,000 fine for the second violation, and criminal penalties, including imprisonment, for the third.

* The Simpson-Mazzoli measure sets an overall immigration limit of 425,000 people per year, while the Reagan proposal does not have a definite ceiling.

* The congressional measure would provide more legal rights to illegal Haitian immigrants requesting political asylum--including the right to be represented by a lawyer--than the administration wants.

In spite of the differences, Attorney General William French Smith yesterday praised the Simpson-Mazzoli bill, saying it "takes us a significant further step."

Meanwhile, Hispanic groups and businesses attacked the measure.

The League of United Latin-American Citizens said the bill is better that the administration proposals, but added that it feared employer sanctions would lead to discrimination against "Hispanic-looking" workers by employers fearful of breaking the law.

The U.S. Chamber of Commerce also opposed the bill, calling the prohibition against employers hiring illegal aliens "both extremely costly and unworkable."

Simpson said he believes the bill has "an excellent chance of passage."