T'S UNFORTUNATE that the Simpson immigration bill, which has just been passed by the Senate for the third time, is burdened with a new and controversial amendment. The provision, sponsored by Sen. Pete Wilson (R-Calif.), would allow hundreds of thousands of aliens to come to this country temporarily for seasonal agricultural work. Sen. Simpson opposed it, Hispanic and labor groups objected vigorously, but agricultural interests have showed increasing strength every time this bill has been considered. This time they won.

Growers, particularly in the West, contend that they need to continue to use illegal workers to harvest perishable crops because they can't find Americans when they need them -- and at a price they want to pay. Under the general provisions of the Simpson bill, employers who hire illegals would be subject to penalties, though growers would be allowed a special three-year phase-out period. After that, alien agricultural workers would be admitted only on special H-2 visas for a specific jobs and a short period of time.

Sen. Wilson hoped to get an open-ended guest worker program authorizing large numbers of agricultural workers to enter for up to nine months, traveling from one work place to another. That version of his amendment was narrowly defeated last week, but a revised version, setting limits on the number of workers who could be admitted at any one time, was adopted Tuesday when Sens. Lugar, Quayle, Rudman, Specter and Riegel changed their votes. Some repair work was accomplished by Sen. Simon on Wednesday; he persuaded his colleagues to close down the program after three years.

There are good reasons to oppose guest worker programs, the strongest being their negative impact on American workers and wages. Sen. Wilson's amendment is particularly objectionable because it requires no government assessment of the domestic labor market before it is implemented. It will not bring in specific workers for specific jobs, but leaves the alien free to move around until he finds work. Rep. Peter Rodino (D-N.J.), author of the main immigration bill in the House, reaffirmed his adamant opposition to the "massive importation of foreign agricultural labor" and will lead the fight against this amendment in the House. On balance, though, and particularly because the program it authorizes is for a limited time, the amendment should not be allowed to kill the bill. Immigration reform is essential and should not be sidetracked by a stalemate on this issue.