A Spanish firm has unveiled a five-year plan for an ambitious commercial and residential project on Biscayne Boulevard near the Arsht Center that supporters say will restart the stalled transformation of the long-dormant, dog-eared corridor into the vibrant, pedestrian-oriented urban district envisioned when the performing arts complex opened in 2006.

The $412 million proposal by Espacio USA, the subsidiary of a big Spanish developer that purchased most of the 1400 block of Biscayne last year, calls for a 12-story office and retail building to start construction early next year on the corner of Northeast 14th Street, facing the Arsht’s opera house. It would be joined later by a separate 650-foot-tall residential, office and retail tower. A tree-shaded public plaza would split the block at a diagonal between the two new buildings.

The 1400 Biscayne project, which goes to Miami’s planning and zoning board for a vote Wednesday evening, would replace a far larger, twin-tower project that had been approved for the site during the downtown condo boom six years ago but, like several other major developments in the immediate vicinity, fell victim to the subsequent real-estate collapse. Some critics feared the previous development’s mass would have overshadowed the opera house.

Espacio is seeking a major modification of that existing development permit, which is still valid, for what is a completely different development, this one designed by Pei Cobb Freed & Partners. The firm, founded by famed retired architect I.M. Pei, was also responsible for the signature Miami Tower, built in 1987 as the CenTrust Tower. Supporters say the new design is far more simpatico than its predecessor to the Arsht and the neighborhood.

“The times have changed, and we didn’t want to take away views or impact the area heavily,’’ said Espacio USA CEO Alberto Muñoz. “We wanted something sustainable that did not overwhelm the city.”

Arsht administrators, who are warily awaiting plans from casino giant Genting, which bought the Miami Herald and Omni buildings nearby, have welcomed the Espacio proposal, a spokesman said.

The proposal would place the 12-story tower at an angle to the opera house’s black-box theater and Biscayne, allowing the arts building to remain visible from up the boulevard. The 55-story tower would also angle back from the street. By placing the 10-story garage at the rear, the architects avoided the usual Miami parking pedestal effect, so that the tower comes all the way down to the street, creating a more pedestrian-friendly ambience. Ground floors of both buildings would have commercial space to provide pedestrian life on the street. The garage would also be lined with usable space on Northeast Second Avenue to avoid the blank-wall, back-of-the house syndrome that deadens some downtown streets.

The complex would begin to provide Arsht patrons with amenities like restaurants and structured parking that have been lacking in the vicinity, backers say.

“It continues the growth and urbanization of downtown,’’ said Alyce Robertson, executive director of the city’s Downtown Development Authority. “It will bring more life into that area around the Arsht and add to the vitality north of Interstate 395, which has been like an invisible line separating the Omni from everything that’s going on downtown.’’