Joe Petronella, a veteran undercover narcotics agent from Buffalo, is sweating bullets. He has spent much of his professional life on the street chasing drug dealers and other assorted lowlifes, and now he has been invited to lunch with President Reagan on Inauguration Day.

"All the people I know are on the street," Petronella, an assistant chief of the Erie County Sheriff's Department, said yesterday. "Now I'm going to meet people for real who hopefully have not used drugs and are straight. Probably the toughest part I'll ever play will be in Washington, playing it normal."

Petronella is one of six citizens from across the country picked to take part in the 50th inaugural luncheon. The affair, which follows the swearing-in ceremony at the Capitol, traditionally has been restricted to the vice president, cabinet members, Supreme Court justices and congressional leaders.

Now the cream of Washington will be rubbing elbows with the likes of Charles L. Stover, a labor official from nearby Lanham; Ernest A. Mass, a San Antonio firefighter; N.F. Plunkett Jr., an Alabama truck driver; Stan R. Ahlerich, a wheat farmer from Kansas; Marilyn Koobation Hamilton, a paralyzed California businesswoman and champion skier; and the shadowy Petronella.

Sen. Charles McC. Mathias (R-Md.), chairman of the Joint Congressional Committee on Inaugural Ceremonies, said his wife, Ann, came up with the idea for expanding this year's guest list to give the luncheon greater meaning for the average American.

"I think it is a more perfect union when a farmer from Kansas and a truck driver from Alabama can come and have lunch with the president," Mathias said.

The guest list offers a happy mix of political persuasions and professions, as well as regional balance. One common denominator seems to be that all the invitees excel at what they do and most have gained national recognition of some sort.

Perhaps the most extraordinary of the group is Marilyn Hamilton, 35, a former high school teacher and sports enthusiast from Clovis, Calif., who was paralyzed from the waist down in a 1978 hang-gliding accident. She went on to help found a state-of-the-art wheelchair manufacturing company and has led a vigorous, athletic life.

"I was a real outgoing person and it was hard for me to relate to a nonactive life style," Hamilton recalled yesterday. "Life is not over. You can go after your dreams and do those things if you just have the desire and the determination."

After her accident, Hamilton joined her family's fruit business for awhile before helping to found Motion Designs, Inc., a manufacturer of colorful, lightweight, aluminum-tube wheelchairs that provide users with maximum mobility. "It's been a real rewarding experience servicing the handicapped," said Hamilton, who will be seated in a bright red Motion Designs model when she arrives in Washington.

Hamilton continued to pursue her interest in tennis and skiing. She was twice crowned women's national tennis champion, in 1982 and 1983, by the National Foundation of Wheelchair Tennis. She also has reigned as a national sit-ski champion for the past four years.

Last May, Hamilton met President Reagan when she received a western regional small business award.

"I'm in awe and I'm humbled and excited about the opportunity to take part in such an historic event," Hamilton said about her invitation to the inaugural luncheon. "It's fabulous."

Stan Ahlerich, a Winfield, Kan., wheat and feed-grain farmer, was attending an American Farm Bureau Federation meeting in Hawaii when Sen. Mathias called his home with the invitation.

"He Mathias called and talked to the babysitter," said Ahlerich.

With his family, Ahlerich, 33, owns 1,600 acres of farm land in south central Kansas. He is chairman of a young farmers and ranchers advisory committee and generally approves of Reagan's farm policies.

But if he gets a chance, he will tell the president he hopes the administration will become more aggressive in seeking new overseas markets for U.S. farmers, and that young struggling farmers will get some extra help.

"They the administration are talking about moving toward a free-market agricultural economy, which I agree with," Ahlerich said. "While they make this transition, the established farmer will do okay. But the young farmer . . . if he has a couple of bad years of weather, he'd probably be out of farming."

Chuck Stover, president and business manager of the AFL-CIO Operating Engineers Local 77 in Maryland, isn't a big fan of Reagan's policies and isn't quite sure why he was invited.

"But it's always an honor to be with the president," Stover said. "You don't have to agree with his philosophy because, after all, he still is the president."

Stover, 55, who lives with his wife, Anne Marie, and three children in Lanham, has been in the labor movement since he graduated from high school in 1947. If he has an opportunity to chat with the president, Stover intends to raise his concerns about the economy.

"It's not all roses and peaches and cream as I think he thinks it is," Stover said. "There are a lot of pockets of unemployment and problem areas out in the countryside. We might be doing all right in Washington, D.C., but a lot of Americans are still on the starving list."

"Butch" Plunkett, 60, a veteran driver for Chevron U.S.A. Inc. of Birmingham, Ala., with an almost unbelievably safe driving record, and "Bud" Mass, a 19-year veteran of the San Antonio Fire Department, also will be at the luncheon.

Plunkett, who during the past 37 years has driven more than 2.5 million miles without an accident, was named 1984 Driver of the Year by the American Trucking Associations. Mass served in the Navy and is active in the Coast Guard Reserve.

The luncheon dignitaries and guests will gather Jan. 21 in the Capitol's floral-decorated Statuary Hall and will be seated at a 26-foot-long head table and 21 round tables.

The menu includes hot mousse of sole and sauteed spinach with a lobster and truffle sauce, medallions of veal with morel sauce, glazed vegetables, wild rice and chestnuts, and a dessert of a cold praline souffle with raspberry sauce. The wine and champagne are Californian.

Petronella, the Buffalo undercover agent, said he was "shocked" and delighted to get his invitation. He hopes to have a word or two with his favorite in the administration -- First Lady Nancy Reagan.

"She's so dedicated against drugs," he said. "She's just so in that drug culture as far as understanding the harm it does . It hypnotizes me."

Petronella has been in the Erie County Sheriff's Department for 13 years and was the National Sheriffs' Association's 1984 Deputy of the Year. He said he has dedicated his life -- even forgoing marriage -- to combating illegal drugs because of their "horrifying" damage to generations of young people.

Petronella has spent much of his adult life working the streets in anonymity, but is prepared to risk blowing his cover to be with the president on Inauguration Day.

"I voted for Reagan, yes," Petronella said. "He's super. I'm an affiliated Democrat, but I'm also a policeman. I think it speaks for itself."