For Ralph Gonzales, migrant worker-turned-restaurateur, the road to Washington is paved with two cases of errant avocados, a set of Mexican pottery smashed to bits by some merciless airport attendants and a switch in political allegiance from the Kennedy camp to Carter's.

But such adventures are mere bagatelles compared with the honor that the San Marcos, Tex., native says came with the opportunity to cook at the White House dinner last night for members of Congress, the cabinet and their spouses.

Gonzales was so honored, as a matter of fact, that it didn't seem to bother him at all that he was invited at the last minute, when a call came from an Austin, Tex., attorney connected with the Carter campaign.

After he decided to accept the offer, Gonzales made another decision. He became a Carter supporter, although he had been a Kennedy delegate at the Hays County, Tex., Democratic convention this year.

As a man who has risen from what a friend called "dirt-floor poverty" to a seat on the county commission, Gonzales may have had more cause for excitement over his invitation to the White House than the other chefs who cooked for the party. His reaction was certainly an enthusiastic one; he claims he was moved to shell out $12,000 of his own money until the folks back home pay him back.

He brought a 10-piece mariachi band and his own food, including four cases of tortillas, two cases of jalapeno peppers ("If it's not hot, it ain't good") and 100 pounds each of cheese and beef. The rest of his money was spent on hotel accommodations and transportation for the 19 people who helped prepare the food.

Gonzales has one of those faces that crinkle up all over when he smiles. He is short and square.He laughs easily.

He began learning to make it in the world when he dropped out of the seventh grade to support his large family. He picked cotton, he worked on a road gang, he drove a sausage delivery truck, he bagged groceries.

But it was the sausage business that intrigued him. He liked the taste of it, he says, and started cooking the stuff at home on Saturdays. When he and his wife, Mary, tried selling their half-pound sausage rolls on the street for a quarter, they made money. And then Gonzales found his calling.

"I had a friend in San Antonio with a taco stand," Gonzales recalls. "I fell in love with it. So I went to a bank in San Marcos and they said there was a taco stand that was going out of business. The bank president said I could take it over. He asked me, 'What are you going to call it?' I said, 'I don't know. Taco Stand.' He said, 'Why don't you call it Pic-A-Taco?' So that's what it's called."

Pic-A-Taco used to be a seven-table operation where the owner did all the cooking. It now has a 200-seat capacity and a full-time cook. Gonzales recently acquired a second restaurant, which he named Don Rafael's. He also owns a construction company.

Gonzales' admirers will tell about him what he himself will not.

"Ralph will bail out of jail anybody who has no friend," said one man who came with the Gonzales crew to Washington. "The number of small loans he's made that he'll never recoup is in the 50s."

If charity is a sidelight, food is his passion. Gonzales describes in detail the art of making flautas, which are tortillas stuffed with chicken and fried in hot fat. He and his crew began rolling the flautas yesterday at 10 a.m. in the White House kitchen.

Gonzales said he was surprised by the size of the presidential kitchen.

"It's pretty small for me to cook in," he said. "But it's real nice and clean. I fell in love with it."