NEW YORK (AP) _ When he walked into the U.S. Embassy in Amman, Jordan, six years ago, Mohammed Salameh was a highly unlikely candidate for a tourist visa - an unmarried, 19-year-old Palestinian refugee making $50 a month.

He couldn't even afford a round-trip airline ticket.

Yet, for reasons that now elude the State Department, Salameh won the local equivalent of the lottery: He got a visa. He came to the United States in 1988 and stayed long after the six-month visitor's limit.

Now Salameh is charged in the bombing of the World Trade Center, raising questions about how he got into the country in the first place.

U.S. embassies and consular offices around the world are supposed to screen out visa applicants who aren't likely to return home, and consular officials can reject such applicants for any reason with no fear of appeal.

In nations from Ireland to the Philippines, this translates into a prejudice against the young, the unmarried and the under- or unemployed.

So how could Salameh get a visa?

A State Department consular affairs official, who spoke on condition of anonymity, said the department could not review Salameh's visa application because such records are never kept for more than a few years. All that's left is a stamp on Salameh's passport.

''It looks like someone made a mistake on him, but we don't know what occurred in the visa interview,'' the official said. ''Something must have happened to make the (consular) officer think he was a legitimate tourist.''

''Maybe, if it was a borderline case, he was very convincing in the interview. Who knows?''

Salameh must have been very convincing. Jordan, like most poor nations, has a high visa refusal rate. In fiscal 1991, for example, the Amman embassy granted 20,163 non-immigrant visas and rejected 18,603 applications.

The embassy's visa application line is one of the longest in town. There are limits on how often people can apply; otherwise, some would apply every day, hoping to luck into a sympathetic interviewer.

The interview usually lasts no more than a few minutes. ''That's your time on stage, and you've got to do something with it,'' explained Allen Kaye, a New York immigration lawyer. ''The presumption is that you're lying. The burden of proof is on you to show you'd come only to visit, not stay.''

Salameh's mother said his family was shocked when he received the visa.

''It was kind of a joke that he even applied,'' she told Newsday. ''He and some friends were complaining about their low salaries ... and they said, 'Why not go to the United States?' Mohammed was astonished to be granted the visa. None of his friends got one.''

Salameh, who was born on the Israeli-occupied West Bank, had worked at a cigarette stand in Jordan. His parents borrowed the money for the plane ticket, Salameh's mother said.

''I'm surprised he got a visa,'' said Denise Sabagh, secretary of the American Immigration Lawyers Association. ''His chances were really marginal.''

Salameh is what is known in immigration law as ''an intended immigrant'' - he entered as a tourist but planned to stay. Relatives said he went to America to find work. He sent home about $5,000 he earned doing odd jobs, his mother said.

Technically, Salameh's visa entitled him only to reach the U.S. border; there, he still could have been turned away. But he, like most visa holders, was waved in.

''WE can't just say, 'We don't like the looks of you,''' said Duke Austin, a spokesman for the Immigration and Naturalization Service. ''The initial gate, the real gate, is overseas.''