DENVER -- It takes truckloads of sweet talk and gumption to convince a city that turning its downtown area into a medium-security prison every August is a great idea. Andrew Shlenker, with his Texas-bred drawl and the self-confidence of a wealthy entrepreneur, has plenty of both.

The smooth promoter is receiving equal doses of blame and credit for the first of five annual Texaco/Havoline Grand Prix races that are scheduled here and feature the type of cars that compete at speeds exceeding 200 mph in the Indianapolis 500. Shlenker's insistence on holding this weekend's race in Denver's civic and cultural center and his success in persuading the mayor and city council to agree have resulted in an 18-block compound downtown.

Chain-link fences 10 feet high line both sides of every major street, obscuring views of the State Capitol, City Hall, historic Civic Center Park, the art museum and the central library. Stacks of bleacher parts and concrete barricades force the elderly to scramble over obstacles at every bus stop and, in one of many embarrassing moments for race organizers, workers had to hustle to remove scaffolding piled on sidewalks frequented by patrons of the state library for the blind.

The city's busiest streets are to be closed beginning tonight. Hundreds of downtown parking spaces have been lost all month to the barricades, sending tourists and city employees on rush-hour searches for scarce space at inflated prices in private lots. City buses have been detoured to a staging area on the road next to the State Capitol, adding disgruntled legislators to the long list of Grand Prix opponents.

Critics have noted that noisy, exhaust-spewing race cars may not project the best image for a city that bans wood-burning stoves on some winter days and is among the most polluted in the nation. Race promoters countered that the high-performance cars run on clean-burning methanol, but their message was muddled when they chose to sell the race with the unfortunate slogan, "The Rockies Are Going to Roar."

Shlenker, son of the former owner of the Denver Nuggets professional basketball team, not only persuaded city leaders to endure the disruption for at least four more Augusts, but he also induced the city to pave the 1.9-mile race course to Grand Prix standards and was granted fire and police protection. The subsidies amount to at least $3.2 million over five years.

Grand Prix promoters smoothed their ride by winning over Mayor Federico Penåa's administration early in the two-year battle to approve a downtown race. Penåa saw the Grand Prix as a piece in his plan to revive an economy that went bust along with oil prices in 1986. Together with a $2.3 billion new airport scheduled to open in 1993 and a convention center that opened in June, the Grand Prix would bring free-spending fans to downtown and showcase Denver's historic civic center on national television, he said.

Penåa's hopes were bolstered by an economic study, financed by Shlenker, that said the race would pump as much as $32 million into the local economy. That study has been toned down since then by a Chamber of Commerce assessment that the Grand Prix would bring only $15 million in new economic activity, but the contradiction has not dampened the mayor's enthusiasm.

"I am very excited about the Grand Prix," Penåa said last week. "Denver citizens over time will realize how exciting this is." Skeptics abounded when the Grand Prix began a downtown race in Detroit, but the Motor City's race weekend has become the largest sales-tax generator of the year, topping even Christmas, Penåa said.

Denver residents have not been as quick to embrace the three-day gala. Polls and a steady stream of coffee-shop grousing about downtown barricades indicate that the general public remains heartily opposed to a city-subsidized Grand Prix, a fact that even Penåa acknowledges.

Businesses also are split in their judgments. Downtown bars are hiring extra workers for what promises to be an eating and drinking frenzy, but other retail stores are complaining bitterly that the month-long obstacle course is hurting sales.

"I think most people will just avoid coming downtown entirely," said Beth Byerlein, general manager of Arapaho Office Express, a large supply store near the race track. Byerlein estimated that she will lose $10,000 in business on race weekend because customers intimidated by barricades will shop elsewhere.

Race spokesman Porter Wharton countered that the Grand Prix has signed reimbursement agreements with 125 track-side businesses and organizations. "We've had {compensation} requests from businesses as far as a half-mile away," he said. "We've just had to draw the line."

Byerlein knows that her vocal opposition is unpopular in a city willing to try nearly anything to revive its economy. "People aren't speaking out because they're afraid of the backlash from going against an economic booster," she said.

The final straw for race critics came recently when it was learned that the telecast of Sunday's Grand Prix would be blacked out locally, since only 45,000 of 55,000 tickets have been sold. Denver residents subsidizing the race with tax dollars and living with the maze of barricades could not even watch the race on television, critics said.

Shlenker's group remains undaunted, saying preparations have gone more smoothly than it had hoped. "We knew going into this that it would be extremely controversial and under a tremendous amount of scrutiny, and we certainly have not been disappointed," Wharton said. "But the controversy has subsided to a tremendous degree."

Shlenker, a former promoter of rock concerts and tractor pulls, has hinted that he plans to expand his Grand Prix network to downtowns in Houston and other cities if the event here is successful. Cities that know what is good for them will boost their economies by following Denver's lead in creating auto races in their most visible and historic centers, he said. Then he added the sort of southern-fried homily that wins over his supporters and infuriates his critics:

"Study the turtle. He makes no progress unless his neck's out."