The project is slated for the southwest corner of Red River and East Cesar Chavez streets. Constellation Property Group has a contract to buy the three-acre site, across the street from the Austin Convention Center, from local developers Perry Lorenz and Robert Knight.

Constellation's condo and hotel towers each would be about 30 stories. The project also would include ground-floor retail and an office building of about eight stories.

Part of the land was once envisioned as the site of a headquarters for software maker Vignette Corp., but that project evaporated with the tech bust. In the past year, however, rising demand for downtown living has spurred new interest in property east of Congress Avenue.

The 13-story Milago condominiums on Rainey Street opened in May. Ardent Residential plans an apartment and condominium high-rise adjacent to the Four Seasons Hotel. High Street Residential is developing a 22-story condominium/hotel project at Red River and Davis streets.

Constellation President Eugene Marchese said he expects the land sale to close in September.

With the necessary zoning in place, construction could start in mid-2007 and take about three years to complete, said Chris White, senior associate for Marchese + Partners International Pty Ltd., which designs Constellation's condo projects.

White said the designs would involve slender towers built above a several-story podium level. The so-called point tower approach allows for high density without blocky, view-obliterating structures.

"They'll be pretty special buildings to anchor that end of downtown," Marchese said.

Marchese said Constellation is negotiating with two hotel operators but declined to identify them, citing confidentiality agreements.

Constellation has another ambitious project in the works, at the northeast corner of Interstate 35 and Riverside Drive. If the City Council approves a needed zoning change today, the company plans to start work soon on the complex, which will have four condominium buildings of descending heights, with an 18-story tower on Riverside and four-story buildings along the shore.

The new downtown project, tentatively named Red River, is bounded on the west by Waller Creek, where city officials are trying to revive plans for a flood control project. The goal is to open the door to development that could result in an Austin version of San Antonio's popular River Walk district of cafes, shops, hotels and other attractions.

Constellation plans to meet with the city next month to discuss Waller Creek upgrades, Marchese said.

"We're excited about what they're doing, and they're certainly going to be excited about what we're doing," Marchese said.

The site's proximity to Waller Creek was one of its selling points, White said.

"Certainly the activation of Waller Creek is a critical element to the success of (our) project and will really open that area up to the public," White said.

Mac Pike, chairman of the Sutton Co., an Austin-based real estate development company, agreed.

"It's a great site that our company has looked at over the years, and we think that a project such as Constellation's could transform that area into a very viable retail/mixed-use destination in downtown."

A collection of small buildings on the site would be razed for the project.

Constellation's project is one of more than a dozen residential projects planned or under construction downtown as the city works toward a goal of having 25,000 people living there in the next 10 years.

As with other downtown residential projects, it costs to live in a vertical neighborhood. Marchese said one-bedroom units could start at about $350,000; two-bedroom units could start between $400,000 and $500,000; and units on the upper floors could range from $1.5 million to $2 million.

Austin is one of four U.S. cities in which Constellation has acquired land for condominium developments. The others are Phoenix, Las Vegas and San Diego.

Marchese founded Constellation 12 years ago in Sydney and has developed about 10,000 condominium units in Australia, he said.