Interview with Spain's unruly colonel

''If the unity and security of Spain is threatened, I will fight to save my country. If the King goes against the integrity of Spain, I will go against the King.''

The star performer of last year's televised coup, Lt. Col. Antonio Tejero de Molina, seemed more like a gracious head of state receiving guests than a condemned prisoner serving out 30 years in a dreary military jail. The man with the three-cornered hat and barbershop moustache, who held the entire Spanish government, Parliament, and nation hostage for 19 hours at the hands of his machine-gun armed Civil Guards, made no bones about his belief in the need for another military intervention.

''If I could do it again, I would,'' he declared unabashedly Sept. 30 from his comfortable living quarters in a military compound outside Madrid, where he graciously agreed to be interviewed.

Two days later, the flamboyant colonel and several other coup ringleaders were all incommunicado for their suspected role in masterminding another wild plot for the eve of the Oct. 28 national elections. Colonel Tejero is now isolated in a military prison in the province of Cartagena and his lenient unsupervised visiting hours are over for a while.

It seems that Tejero's visitors were more than simple well-wishers. The three colonels arrested by the Spanish government last week for allegedly planning the Oct. 27 coup were apparently ''regulars'' of Tejero and the other condemned coup plotters.

The government also plans to investigate Tejero's newly formed political party, Solidaridad Espanola (Spanish Solidarity), on grounds that it may have been part of civilian cover for the coup plot, Defense Minister Alberto Oliart said Monday.

Two days before Tejero's isolation, when this reporter interviewed him, the usual assortment of visitors was lined up outside the gates of the military post where Tejero was the lone deluxe prisoner. There were obvious and vociferous members of Spain's far right brandishing right-wing and fascist emblems whom the military gate guards termed ''the regulars,'' wives and family members of Civil Guard officers, two ladies dressed in black with baskets of home-baked goods, and members of Tejero's Solidaridad Espanola, who helped arrange my interview.

Tejero was not allowed to receive journalists so I was warned to pose as ''a friend.'' Gate guards collected identification cards and routinely wrote down ''friend'' or ''admirer'' on entry forms. We were to state profession or job, to which I replied ''a mother,'' without having to lie. Tejero, however, knew the real reason for the visit, I was assured.

We were led to a specially prepared visiting room where il17l,0,16l,6pother soldiers searched us for arms. An obvious right-winger, complete with a golden Tejero key ring, had his briefcase full of papers searched only for arms, not documents.

Finally, my turn came, after a rural and evidently poor family from a province. This group had come to Madrid several times to visit its hero and always brought homemade almond candy. They got five minutes with the busy colonel, who has a policy of not turning anyone away. Tejero has been receiving up to 200 visitors per day and, by his own estimates, greeted 32,000 since his arrest Feb. 25, 1981.

Tejero's receiving room at first glance seemed like the modest living room of any provincial Spanish middle-class military family. Military decorations and family pictures decorated the walls. A large color television and long shelf of videos apparently helped him pass the time.

Knowing he was a celebrity, Tejero was open to questions. He professed a 19 th-century military code of patriotism and assured me that he was always at the service of his country and more than willing to sacrifice himself again if necessary. Unrepentant of his famous assault on Parliament, he boldly affirmed, ''Of course I would do it again. I will never pass a bill for my sacrifice.''

''National unity and the integrity of Spain is threatened again by terrorism and Marxism,'' Tejero argued. He claimed that granting regional autonomy was ''intolerable'' and was ''threatening to disintegrate the fatherland.''

What was of greatest concern, however, was the ''stink of Marxism.'' ''Every time I smell it I must fight,'' he explained. The possibility of a Socialist victory in coming national elections posed a threat, according to Tejero, who affirmed, ''We must work for sufficient force to throw them out of the country.''

Tejero saw no distinction between socialists and communists. Socialists are ''better prepared and better disguised these days,'' he added. But they are ''Marxists, Marxists, Marxists,'' he added, in case I had missed the point.

Admittedly not a believer in democracy nor a constitutional monarchy, Tejero was in favor of restoring the ''type of organic democracy we had under Generalissimo Franco.''

Although not in favor of Spain's membership in NATO ''which could wait a while until we solve our internal problems,'' Tejero hoped he might find support in the United States in his fight against Marxism in Spain. He admitted, however , he had had no contact or indication of US support for his cause, although he did say he ''appreciated'' former Secretary of State Alexander M. Haig's initial description of Spain's aborted coup as an ''internal affair'' of Spain.

Tejero has managed to cultivate contacts and friendships unhindered. Evidently, he has even managed to conspire freely. The Spanish press has expressed outrage over his lenient, if not superstar, treatment. He looked in good physical shape, having jogged mornings to keep trim and tanned. The colonel was allowed to dine regularly with his wife and daughter, and their meals were served by soldier-waiters.

Now in a military garrison in Cartagena, his social schedule will be more restricted - at least for a while.