Leaders of several Hispanic groups said yesterday they will work to try to defeat a major revision of the nation's immigration laws unless the bill is stripped of a provision imposing sanctions on employers who knowingly hire illegal aliens.

The sanctions provision would leave employers reluctant to hire anyone who looked foreign, increasing job discrimination against Hispanics and others, the opponents said.

The opposition was voiced by leaders of the League of United Latin American Citizens (LULAC), the Mexican American Legal Defense and Educational Fund (MALDEF) and other Hispanic organizations. They helped block a similar immigration revision bill in the House late last year.

Their threat came on a second day of hearings on the bill, which would be the first major alteration of immigration laws since 1965, if enacted. The sanctions provision would require employers to verify the legal status of all persons hired and would impose civil and, in some instances, criminal penalties if illegal aliens were discovered on their payrolls.

Proponents of the bill, including sponsor Sen. Alan K. Simpson (R-Wyo.), have said that the sanctions are an essential trade-off if the bill is to include another provision strongly favored by Hispanic groups: amnesty for millions of illegal workers in the country.

Yesterday, the Rev. Theodore M. Hesburgh, former chairman of a special federal study commission on immigration and refugee policy, compared the amnesty program, employer sanctions and proposed stricter border controls--the three major parts of the bill--to the legs of a stool.

"It seems to me that stool can only stand on three legs--you're going to get all three of them or you're going to get none at all," Hesburgh told the Senate immigration and refugee policy subcommittee, of which Simpson is chairman.

But Hispanic leaders who followed said they could not support the bill as drafted. They said they favored a stricter policy of enforcement of current immigration laws instead of the proposed new sanctions.

LULAC executive director Arnoldo S. Torres said if the sanctions provision is included in the proposed new revision, "then the alternatives we have are virtually nil but one: to work once again to defeat this legislation."

Simpson told Torres, MALDEF president Joaquin Avila and other Hispanic leaders, "There will be no legislation without employer sanctions" and urged them to compromise.

Yesterday, the Hispanics picked up an ally on the employer sanctions issue. The American Bar Association reversed a position it has held since 1976 and urged rejection of the sanctions.