The Reagan administration is asking Congress to give the president extraordinary emergency powers to keep unwanted immigrants off U.S. shores. It has also proposed that the power of the courts to review immigration decisions for fairness be sharply curtailed.

In an effort to prevent a recurrence of last year's influx of 140,000 Cubans and Haitians into southern Florida, President Reagan--as part of a top-to-bottom revision of immigration laws--is asking for authority to declare an emergency that could last as long as one year and would involve many special powers:

The president could order the sealing of any harbor, port, airport, road or "any other place, structure or location" to prevent unwanted aliens from getting into the country.

He could restrict travel by Americans, both domestically and to a country named in an emergency declaration. He is asking for authority to forbid any type of boat, vehicle or aircraft to go within a certain distance of the designated foreign country.

Aliens apprehended could be put into detention camps to await deportation hearings, and they could only be released at the discretion of the attorney general. The attorney general could transfer the immigrants from one facility to another at will, and no court would have authority to review his decision.

In setting up the detention camps, the president could exempt the government from virtually all environmental laws, and from all other federal, state and local law intended to "protect or preserve the environment, wildlife or aspects of the history or heritage of the United States." In at least one case recently, lawyers fought creation of a detention camp by saying the government had not made an environmental assessment as required by law.

The president is asking authority to board foreign vessels on the high seas to search for illegal aliens without authority of the foreign country--which the administration acknowledges is a violation of international law. In an accompanying explanation, the administration says, "Such action inconsistent with international laws, and it is not anticipated that the United States would violate those customary rules of international law...except in the most compelling of circumstances."

In enforcing the emergency provisions, the president would be authorized to call for assistance from the Army, Navy and Air Force, as well as state and local agencies, and he could empower them to assist activities including the seizures of vessels, arrests, and detention.

The legislation would allow the president to declare the emergency situation any time he determines that "a substantial number of aliens who lack documents authorizing entry to the United States" are either on their way or about to embark. The legislation includes an authorization of $35 million to pay for the emergency measures.

Reagan is asking that illegal aliens' access to the federal courts be sharply curtailed.

Some would-be immigrants are already turned back at borders by customs officers. Others--those affected by the proposed legislation--fall into three classes: those who are seeking asylum; those not turned back but picked up before they cross U.S. borders who are subject to exclusion hearings; and those apprehended inside the country either without documents or with expired documents, who are subject to deportation hearings.

Right now, all are being given access to as many as five layers of review by the Immigration and Naturalization Service and then by the federal courts. This right to review is being used by lawyers to delay expulsions; tens of thousands of cases are backed up.

Reagan is seeking to have asylum hearings handled by an asylum officer at INS with no judicial appeal.

He would have exclusion hearings handled entirely within INS, with an original hearing and then a single appeal to an immigration judge within the service.

Persons subject to deportation would still be allowed to appeal to the federal courts, but they would have to appeal within 30 days rather than the current six months.

The immigration package, which includes provisions to eventually legalize up to 6 million aliens who are already here illegally, was outlined by Attorney General William French Smith in late July, but the actual legislation, including the provisions for the emergency powers and the reduced judicial review, was just beginning to circulate yesterday on Capitol Hill.

Sen. Alan K. Simpson (R-Wyo.), chairman of the judiciary subcommittee on immigration and refugee policy, said he had neither heard about nor seen the provisions for emergency presidential powers. He said he would disapprove of any attempt to allow denial of asylum without some sort of appeal.