The news from here is usually bad, so bad that Detroit has become a handy symbol for the problems of urban America. This time last year the city government was talking about turning off the street lights early to save money. Six months later, after the city had laid off 20 per cent of the police department, teen-aged gangs with names like the Black Killers and the Earl Flinns (sic) terrorized a concert crowd at the city's riverfront Cobo Hall. The city recently enjoyed an unusual six-day hiatus from homicide, but downtown was jolted Thursday when a middle-aged Detroiter was shot as he waited for a bus near a downtown department store during the noontime rush.

Through it all, with their backs almost literally to the river, people with a stake in Detroit have looked hopefully, almost desperately to a massive building project just up river from Cobo Hall called Renaissance Center. For the past five years, ever since Ford Motor Co. chairman Henry Ford II announced the $337-million hotel and office complex, it has been viewed by many of Detroit's best hope, at times the lone symbol of the city's hope for rebirth.

Ford persuaded 50 other Detroit area businesses to invest in the project an announced earlier this year that 1,700 Ford employees will be transferred from the firm's world headquarters in Dearborn to one of Renaissance Center's four office towers.

At the opening this week of the 73-story Detroit plaza, perhaps the world's tallest hotel and clearly the centerpiece of Renaissance, Detroit Mayor Coleman A. Young said:

"Today is a great day for our city and for cities all over America. This (Renaissance enter) is a monumental statement that speaks for itself. Our cities are indeed alive and on the upsurge. There is no better answer to the doubters and the crepe hangers."

The Detroit Plaza, designed by Atlanta architect John Portman, is compelling - as hotel if not as symbol. At its core is an eight-story atrium lobby filled with 5,000 grape ivy plants, 3,000 philodendrons, 180 weeping fig trees and 33 kentia palm trees. Visitors can gaze up at all that foliage, which is suspended above a half-acre lake, from the INner Circle Lounge, which revolves around the base of the hotel. Or they can view it all from above, in one of a dozen "cocktail pods" which just over the lake.

"This place is a museum," exclaimed 18-year-old Paul Schneider the other day as he breezed through the lobby with two of the pals from Grosse Pointe South High School. The group had heard too much about Renaissance Center to pass up the first chance to see from themselves. So they skipped school and came downtown for the opening of THe Plaza, Detroit's first new hotel in 12 years.

"Everything inside," Schneider observed, "look like it's outside."

That, of course, is what Portman had in mind.

In addition to the Detroit Plaza, Portman has designed the $150-million Peachtree Center in Atlanta, the $200-million Embarcadero Center in San Francisco, the Hyatt Regency O'Hare in Chicago and the Bonaventure Hotel in Los Angeles.

Either the Plaza or Peachtree is the tallest hotel in the world, depending on whether you measure from the sidewalk or the basement. Western International Hotels, which runs them both, gives the tallest title to Detroit.

As grand as the plaza may be, it is not without its critics.

To create the spiraling staircases and swirling effect in the atrium, Portman has used an awful lot of reinforced concrete - a material which permits nice lines but doesn't offer much warmth.

Outside, Renaissance Center is separated from Jefferson Avenue by 30-feet high concrete beams which house the heating, cooling, ventilation, fire safety and security units for the Center. They also wall off the center from the city, creating an impression of a kind of fortress.

"In an ideal world some of the physical barriers would not be needed," Detroit City Council president Carl Levin said, "but in the real world they are a necessary compromise so the feeling of security would be there."

Of Renaissance he said, "It's an absolutely overwhelming experience to be there. When people come to behold what is there I think it's going to have a very positive impact, a contagious effect downtown."

Many of the tenants in the center's office towers have moved there from older downtown buildings, but the city hopes this Center will eventually enable downtown to compete more effectively with suburban office buildings.

Paul Green, a 37-year-old Detroit attorney, considered moving to a suburban building before deciding on a 20th-floor suite in Renaissance. The rental rate is roughly the same as what he paid in an older downtown building, and now he had a view of the ice flows making their way toward the Ambassador Bridge from Lake St. Clair and Lake Superior.

"It's just a trip being here," he said.

There are some who believe it will ripple regeneration all across town. Larcenia Posey, 50, a Detroit homeowner, said after the opening:

"This is goin gto make peope want to better their own conditions. When I go home I'm going to feel like planting a tree or putting in some flowers." CAPTION: Picture, The 73-story Detroit Plaza, part of the $337-million Renaissance Center on the city's riverfront.