The Reagan Cabinet has approved changes in a comprehensive immigration policy package that some officials fear tilts the plan toward the economic desires of western employers who hire illegal workers.

The Cabinet reached agreement on the final and most contentious components of the plan Thursday, accepting White House staff proposals to reject use of an identity card that would make hiring illegal aliens more difficult and to expand an amnesty provision to cover up to 5 million current illegals, Justice Department and White House officials said. President Reagan is expected to formally approve and announce the package after his return from Ottawa this week.

The Cabinet has held four meetings on the complicated immigration package in the last three weeks. Some Justice Department officials feel the waiting has cost the administration any real chance of getting accompanying legislation through Congress before it stalls for next year's elections.

A decision on the politically volatile policy has been delayed because some White House officials, chiefly domestic policy adviser Martin Anderson, disagreed with and finally got the Cabinet to modify the sanctions and amnesty recommendations of a Cabinet task force headed by Attorney General William French Smith, sources said.

Agricultural interests from the western states that are the backbone of the president's political support have opposed sanctions against employers who hire illegals. Rejection of the task force's recommendation for an identity card -- actually an enhanced Social Security card -- is seen by several officials as a significant weakening of the sanctions provision, because it will make it more difficult to verify the legal status of a new employe. One White House official said yesterday the decision on the card was based more on philosophical and budgetary considerations.

The westerners also have pushed for a large Mexican "guest worker" program, and the increased numbers of illegals eligible for the amnesty povision will be viewed with enthusiasm by western politicians, one official said, because it is "simply a guest workers program by another name." A White House official rejected the criticism, noting that many of the current illegals already have jobs and wouldn't displace American workers.

A White House official insisted that the total package still is balanced between enforcement and new opportunities for legal employment. A July 10 memo for the Cabinet said the plan should reduce net illegal immigration from 500,000 to 100,000 a year. But it also referred to enforcement mostly in terms of perception and an "image of control."

A pilot guest worker program of 50,000 Mexicans for each of the next two years also is part of the immigration package, as are sanctions against employers who "knowingly" hire illegal aliens, officials said. Sen. Paul Laxalt (R-Nev.), a close friend of Reagan, and some other western senators reportedly met at the Hwite House Friday in an effort to increase the numbers in the pilot guest worker program, but no major changes from the 50,000 figure are expected, a White House official said.

Instead of the task force's enhanced Social Security card, the administration will propose that employers and workers merely sign a form certifying that the worker is a legal resident of the United States, officials said. Sen. Alan R. Simpson (R-Wyo.), chairman of the Senate Judiciary subcommittee on immigration, expressed concern Friday that this method of verification is not secure enough.

"Sanctions won't work without it," he said. "I guess verification will have to come out of the hearing process . . . Every time someone talks about this issue they flee to the Statue of Liberty. I want to hear alternatives. We'll consider everything but tattoos." Simpson said he plans to begin hearings before the August recess, although he canceled a Monday hearing to await Reagan's announcement.

The amnesty process also was modified from the original task force recommendation, which had proposed a two-tier legalization process covering an estimated 2.7 million aliens. The newly agreed plan would cover an estimated 5 million illegals -- any illegal alien living in the United States as of Jan. 1, 1980 -- but also would impose new restrictions, officials said. The task force envisioned a five-year wait before illegals could become permanent residents and eventually citizens. The Cabinet tenatively approved a 10-year waiting period before allowing anyone to apply for permanent residence.

In addition, the new plan forbids amnesty-seekers from bringing other members of their families into the country, and it requires the alien to have a minimal knowledge of English before becoming a permanent resident. These provisions are likely to be fought by Hispanic groups which have favored amnesty.

In the July 10 memo to the Cabinet, Craig R. Fuller, director of Cabinet administration, described the proposed new status as "renewable term temporary resident" and said it would eliminate the subclass of illegals in American society. He noted it also would be critized for not significantly impeding future flows of illegals, and said the English language requirement would be impractical for older people.

Other elements of the policy had been decided earlier, including strict measures to prevent a recurrence of last year's flood of Cubans and Haitians into south Florida. There are plans to negotiate with Haiti on stemming the flow from that country, to selectively interdict boats on the high seas, and to detain newcomers indefinitely in what the administration recognizes could be called "concentration camps."

Proposals to move hard-to-settle Cubans from Fort Chaffee, Ark., to Texas or Maryland have been stymied by political opposition, although the package includes a proposal for a permanent detention site for emergencies. The continuing volatility of that issue was illustrated Friday when Florida filed suit against the federal government, despite its plans to move Haitians out of the state. The state sued, officials said, because the federal authorities wouldn't promise never to house the illegal entrants there again.