Have you ever heard of Harlingen? Hardly anyone has, outside of Texas, where it is. But something has happened to Harlingen, with relation to something that might happen there, although little has since the 1800s when it was known as "Six-Shooter Junction" because guns outnumbered residents.

Harlingen is now enjoying the 15 minutes of celebrity that Andy Warhol said is due everybody. Its booster was none other than the president of the United States. On March 4, at a White House meeting with leaders of the Nicaraguan contras, President Reagan pointed a golden finger at the town of 43,000 just 28 miles from the Mexican border.

Failure to fund the contras, he warned, would mean "consolidation of a privileged sanctuary for terrorists and subversives just two days' driving time from Harlingen, Tex."

That bit of travel information was perhaps a lurch toward reformulating an old Vietnam war alarm -- if you don't fight them in the elephant grass of Saigon, you'll have to fight them in the rye grass of Oregon.

Whatever the presidential impulse, Harlingen Mayor Samuel Lozano is busy fielding telephone calls from reporters around the country.

Personally, Mayor Lozano, a Democrat and retired educator, does not fear invasion from the south. "If the president knows there is a danger, he should do something about it," he said in a telephone interview, "including the use of military force to stop it."

It is the mayor's view that the $100 million in proposed contra aid would be better used to beef up the Immigration and Naturalization Service so it could stem the tide of illegal aliens, and drugs, which, said Lozano, are far greater perils to Harlingen.

Like everyone else, the mayor is baffled by Reagan's designation of Harlingen as the Omaha Beach of the Sandinistas. The only connection anyone can figure out is a 1980 Reagan campaign stop. Apart from a muddled reference to the Mexican patriot Miguel Hidalgo, whom he mistakenly identified as "a brave American priest," the visit made little impression on anyone.

Reagan's suggestion that it will become the beachhead to feel the first wavelets of the "sea of red, eventually lapping at our own borders," has inspired this free-verse reply from Texas poet Mary Connell, sister of House Majority Leader James C. Wright Jr. (D-Tex.):

"Does he anticipate that they will pile into station wagons

and undertake to prove it can be done,

driving hard through Honduras and Guatemala down pock-marked roads,

past frontier guardsmen and customs agents . . .

pressing upward, ever upward through the scimitar of southern Mexico . . .

without taking time to smell the flowers or visit the ruins . . . . "

It is Connell's fancy that the invaders, when they get to Harlingen, will find nothing better to do than descend on a Dairy Queen "for a real cheeseburger, large fries and a cone with a curl on top."

Connell's confection caused much hilarity when her brother read it aloud to a news briefing in the House Speaker's office.

Let us assume for a moment that the president is right, and that Harlingen stands in peril, not of touchy Latin motorists in station wagons, but of ancient taxis transformed into armored personnel carriers by Soviet steel, stuffed with Soviet ground-to-air missiles, Cuban bombs, bullets and Cubans. Let us suppose that Nicaraguan President Daniel Ortega himself leads the column, that it passed through Mexico undetected, rolled over roadblocks and immigration checkpoints and, having done the journey in the two days, thunders down the highway, not to storm the DQ, but City Hall.

Do not panic. In Harlingen, they will get as good as they give. Consider the Marine Military Academy, a boarding school for teen-age boys "willing to accept strict discipline." Can't you see those junior high warriors shinnying up the palm trees, fired up to pick up extra credits for picking off commies?

Or, as a fallback, consider the "Confederate Air Force Flying Museum." It is, despite its name, dedicated to the preservation of World War II combat planes, many of them "in flying condition." The museum guards could roll out the old crates, rev them up, and strafe the terrorists, shouting "Remember the Alamo" -- although possibly in Spanish, as the population of the district is 60 percent Hispanic.

Maybe the president knew what he was talking about.