WALK into any bookstore in the United States and the works of Nobel Prize-winners Gabriel Garcia Marquez of Colombia and Pablo Neruda of Chile will be easily available. Anyone who wants to can buy Mexican novelist Carlos Fuentes's works or those of Italian writers Alberto Moravia and Dario Fo. And the titles of books by English novelist Graham Greene are almost household words in this country. Yet each of these acclaimed writers, and many others as well, has on at least one occasion been denied an entry visa to visit the United States.
The law responsible for this policy is a section of the McCarran-Walter Immigration and Nationality Act of 1952, which some people would like to change. A bill has been introduced in Congress to do just that.
''Section 28,'' as it is called, empowers consular officials to refuse non-immigrant visas to foreigners who are or have been members of ''communist'' or ''anarchist'' organizations, as well as those who merely ''write, publish . . . circulate, display, or distribute . . . any written or printed matter advocating or teaching opposition to all organized government. . . .''
The exclusion of writers from the US on ideological grounds can take place for a number of specific reasons. According to data collected by PEN, an international association of writers with offices in 55 countries, Gabriel Garcia Marquez was denied entry to the US from 1963 to '71 because of his affiliation with the leftist news agency La Prensa. Since that time, he has been granted entry only on presentation of a formal letter inviting him to a specific event. Last month, Mr. Garcia Marquez was denied entry into the US to speak at a meeting in New York on US policies in Latin America. Finally, in late April, he was granted a multiple-entry visa for one year.
Pablo Neruda, the late Chilean poet and diplomat, was denied entry on the basis of his membership in the Chilean Communist Party. This ruling was waived on two occasions, in 1966 and '72, as a result of petitions put forward by PEN.
Since 1961, Carlos Fuentes, the Mexican author and politician (who virtually grew up in Washington where his father was Mexican ambassador), has either been denied a visa to the US or issued restricted visas, even though he has been invited on numerous occasions to make public appearances under the auspices of respected institutions. He has received an honorary degree from Harvard University and was recently a visiting scholar at Princeton University. PEN has been unable to pinpoint the motive for his perennial exclusion.
Why do Mr. Fuentes and others continue to acquiesce to the indignities and red tape of repeatedly applying for visas?
''If we didn't, we would be giving in to the negative and isolationist spirit of the law,'' says Mr. Fuentes in a statement made available by PEN. ''And we would be denying our solidarity with those individuals and institutions in the USA that so steadfastly seek the removal of Section 28.''
As part of this removal effort, PEN and the Fund for Free Expression sponsored a conference on April 30 at St. Peter's Church in New York, where prominent American authors read from the works of some excluded writers. Present were writers William Styron, Susan Sontag, Arthur Miller, Carolyn Forche, and John Irving, as well as Patricia Derian, assistant secretary of state for human rights and humanitarian affairs in the Carter administration.
''It's a scandal and a hateful thing for a democracy to perpetuate this kind of exclusionary policy,'' Mr. Styron said. ''It allows the United States to be branded as a bigoted nation filled with hysteria about communism.''
Both Arthur Miller and John Irving raised the specter of McCarthyism. ''I doubt strongly that this law could have been passed before 1952, the wildest time of McCarthyism . . . but it's hung on the books because most people aren't aware of it,'' Mr. Miller said.
''I hope it's clear that we would improve our national character by ridding ourselves of these vestiges of McCarthyism which shame us today,'' Mr. Irving said.
Carolyn Forche remarked, ''I am puzzled as to why my government is afraid of a free exchange of ideas. I would hope that my country and its institutions are strong enough to endure freedom of expression.''
Other voices speaking out against the McCarran-Walter Act include the American Civil Liberties Union (ACLU). Its Center for National Security Studies Project has scheduled a meeting to call further public attention to the act on Sept. 18 at the Shoreham Hotel in Washington, D.C. According to ACLU spokeswoman Debra Trevino, a number of foreign writers are expected to attend. Concurrently, writers who cannot enter the US but who are allowed into Canada will convene at the border. Their comments will be broadcast live at the meeting.
Significantly, supporters of Section 28 have been much less vocal than those against it. ''There has been a major step-up in visa denials during this administration,'' Ms. Trevino noted. ''I'm sure there's support of this law out there, but we can't find anyone who will represent the administration in its support.''
In response to this reporter's inquiries, a State Department spokesman declined to comment on the act or on efforts to amend it.
Support for the existing law was recently expressed on ABC's ''Nightline'' by Roy Cohn, counsel in the early 1950s to the Senate's Permanent Investigations Subcommittee headed by the late Joseph R. McCarthy: ''This law is aimed at people who present a threat to national security. Under various circumstances they should not be let in. They have access to courts where their visa denial can be overruled.''
According to Duke Austin, on the staff of the general counsel of the Immigration and Naturalization Service, ''When people are denied a visa, they are required to request a waiver, under provisions of the 1977 McGovern Amendment. Waiver applications take two weeks to process, and 99 percent of them are granted.'' PEN disputes this claim and says that roughly 25 percent of the waivers are denied.
All sides are in agreement that it is primarily terrorists, instigators of violence, criminals, drug dealers, and the like who should be denied entry to the US. ''If the act is amended,'' Mr. Austin explained, ''the judgment as to the motives for visiting the US could be made without the need for a visa denial and a waiver by the consulate in question. We would support that. The law could be modernized.''
Legislation to amend Section 28 has been introduced in Congress by Rep. Barney Frank (D) of Massachusetts. Mr. Frank's bill would, among other things, narrow the national-security grounds for exclusion in order to prevent misuse of Section 28 for political purposes. Hence aliens would no longer be prevented from entering the US solely on the basis of their political beliefs. Hearings are scheduled for June 14, but Representative Frank is doubtful that this measure will pass this year or next. ''The administration has not yet taken a position on my bill,'' he said.
Opposition to Section 28 of the McCarran-Walter Act has a long history. In 1952, President Harry S. Truman vetoed the act, remarking, ''Seldom has a bill exhibited the distrust evidenced here for aliens and citizens alike.''
Congress overrode Mr. Truman's veto.