The citizens of Harlingen would like to know what kind of car President Reagan drives. They are also curious as to whether he ever stops to stretch his legs during long trips. And they wonder if perhaps he exceeds the speed limit when he hits the open spaces. Answers to those questions would help them figure out what Reagan meant recently when he declared that Nicaragua was "a privileged sanctuary for terrorists and subversives just two days' drive from Harlingen, Tex."

The driving distance between Harlingen, distribution hub of the Lower Rio Grande Valley, and Managua, capital of Nicaragua, is 2,028 miles. The highways have two lanes and a variety of obstacles: roadside burros, cows, dogs and bicyclists. There are circuitous routes through mountains and tedious stretches across deserts. Choluteca. Tegucigalpa. Guatemala City. El Jocote. Telixtlahuaca. Puebla. Mexico City. Ciudad Victoria. Matamoros. Brownsville. Harlingen. Not an easy trip, as thousands of illegal aliens can attest. Experienced truckers take three to four days. Three days is pushing it.

"You've gotta have it floored the whole way and never stop to make it in two, I would think," said David Allex, president of the Harlingen Chamber of Commerce.

"I looked at the map the other day and shook my head," said Mayor Samuel Lozano. "You have to drive through the mountains of Honduras and Guatemala just to get to Mexico, and then it's 1,200 miles through Mexico. I would say that trip would tax a person."

It has now been almost two weeks since the president placed Harlingen into the realm of geopolitical rhetoric, and people here are still baffled by both his statement and the attention it has received. With a key congressional vote on Nicaragua coming up this week, national columnists and cartoonists have had a fine time playing with the idea of this quiet, unprepossessing city, 18.6 miles from the Mexican border, as a first line of defense against the Sandinistas. The Marine Military Academy and Ghost Squadron of the Confederate Air Force, two local outfits with defense connotations, have gotten more publicity than they have had in years.

But here the whole thing is no big deal.

The local daily newspaper, The Valley Morning Star, has run one line about the episode, and that was in a wire story from Washington. "Why should we make anything of it?" asked Edd Clark, city editor. "It was just another politician running off at the mouth. Personally, I'm more concerned about Republicans and Democrats than I am about Marxist-Leninists. I think the only reason Reagan mentioned us is that Harlingen was the closest place to the border that had enough Re- publicans to make it worth defending."

Harlingen, though it elects Democrats locally and is 70 percent Hispanic, is Reagan country. The city and Cameron County went for him in 1984, and Harlingen promised enough support in 1980 to bring Reagan down for a campaign stop. It is not by accident that Phil Gramm, the Republican senator from Texas, has his district office here. But when it comes to Central America, specifically whether the United States should send military aid to the rebel contras seeking to overthrow the leftist Nicaraguan government, Harlingen appears to be no different from Congress and the rest of the country: unconvinced.

"I support President Reagan on some things, but I think we're meddling a little too much in the affairs of other countries right now," said Rodric Morrogh, a safety engineer, as he strolled through the Valle Vista Mall. "I understand the danger of communism, but you don't fight it with guns. The Soviet Union can match us dollar for dollar on guns. But they can't compete if we help clothe and feed the poor people."

Seated on a wooden bench inside the mall that day were two retired men who had moved to Harlingen from Chillicothe, Ill., the home district of House Minority Leader Robert H. Michel.

"I don't want the commies creeping up through our back door," Byron Brumhead said. "But I've never really worried about them Nicaraguans coming up here to Harlingen. The problem isn't invasion. They move slowly, the communists. It's a slow buildup, and they're here and you didn't even know it happened."

"I'm kinda for stopping them right there in their country," Homer Gill said. "My wife, she's against it. She thinks her grandchildren will end up in the war."

Down the highway a few miles, at the Harlingen Country Club, home of the Life Begins at Forty golf tournament, retired doctors Robert Stein, formerly of Lincoln, Neb., and O.G. Linimon, formerly of Houston, said they were not especially concerned that Sandinistas might cruise up the Pan American Highway, invade Harlingen and delay their morning tee time.

"You have to understand one thing about us," Linimon said. "We're retired people. We don't concern ourselves with politics anymore. We have nothing to say about Central America one way or another. All we want to do is play golf. I don't think anyone's gonna invade this golf course, at least not in my lifetime."

Lozano, the Democratic mayor, said he appreciates the publicity Reagan has given his city, but he is more concerned about drug trafficking than about possible terrorist attacks. "That's the real problem here now," Lozano said. "The drug smugglers have found this area a little bit unprepared to deal with them."

Silvestre Reyes, chief of the Border Patrol in the Rio Grande Valley, said drugs are moving across the river at an unprecedented rate. In 1985 his agents in this sector made 159 drug seizures worth $6.7 million. So far in 1986 they have made 287 seizures worth $28.8 million. Reyes said his agents arrested more illegal aliens this February than during any month in history. Among the 10,289 illegals arrested last month were 1,100 from Cen- tral America. The patrolmen are on the lookout for terrorists, Reyes said. "We have certain profiles to watch for."

At the edge of Harlingen on Highway 77, the route up from Mexico, stands the Texas Tourist Bureau, a gleaming new facility with a reflecting pool, brick courtyard and red-white-and-blue bunting. "Bienvenidos a Texas," reads the sign outside. "The friendship state welcomes visitors to this land of contrast . . . land of cotton fields and citrus groves, mile-high mountains and semitropic valleys, rolling sand dunes and booming oil fields. Texas, blend of drawling cowboy and city sophisticate, old world charm and progressive ideas, thrill-packed rodeos and gay fiestas. Descrubra Texas Para Un Mundo de Differencia."

Inside the tourist office, Sam Martinez, the manager, said he has seen Nicaraguans there on occasion. "I would say very seldom do we get them," he said. "They are illegal aliens, mostly. They huddle over there near the drinking fountain and take turns using the facilities."

Staff researcher T. James Munoz contributed to this report.