A redesign of Pennsylvania Avenue in front of the White House -- a stretch of pavement marred by concrete security barriers, police cars and guard booths -- received preliminary approval yesterday from the National Capital Planning Commission.

Before construction begins, the plan requires two more votes by the planning commission, an environmental assessment and the approval of the Commission of Fine Arts.

Also yesterday, the planning commission gave preliminary approval to design concept for an Air Force memorial that would be built on three acres now occupied by the Navy Annex adjacent to Arlington National Cemetery and just west of the Pentagon.

The design calls for three spires of steel and is intended to evoke soaring images of flight and provide a visual gateway from Northern Virginia into Washington's monumental core. The memorial was designed by architect James Ingo Freed, the designer of the U.S. Holocaust Memorial Museum.

The memorial is scheduled to go before the Fine Arts Commission this month. Officials of the Air Force Memorial Foundation expect the memorial to be completed in September 2006. About $33 million of the $38 million needed to construct the memorial has been raised, mostly from the aerospace industry but with the help of about 140,000 individuals, according to the foundation.

The plan for Pennsylvania Avenue would transform the two-block segment of America's Main Street that has been closed for security reasons since 1995. It would remove the clutter of concrete Jersey barriers and planters and a small area off 15th Street NW that has become a makeshift parking lot. It would add a line of trees along the sidewalk in front of the White House as well as sleek, retractable steel bollards and redesigned guardhouses.

"This is a real step forward for America," said Richard L. Friedman, planning commission member and chairman of the Interagency Security Task Force created by the commission to incorporate safety concerns in the planning of federal buildings. He called the state of Pennsylvania Avenue in front of the White House "not reflective of our history or our democratic values. It's insulting to the public."

Before the commission voted, a few people spoke against the design, mainly because that part of Pennsylvania Avenue would remain closed. "We continue to oppose restricting vehicular traffic in front of the White House," said George Oberlander, who represented the Committee of 100 on the Federal City and the National Coalition to Save Our Mall. He said the avenue should reopen with a prohibition on large vehicles or trucks. "Those are the security concerns," he said.

Pennsylvania Avenue in front of the White House was closed to traffic soon after the April 1995 bombing of the Oklahoma City federal building. Only bicyclists, pedestrians and authorized vehicles are allowed to enter between 15th and 17th streets. But even before the 1995 bombing, some stubby concrete bollards were erected -- in 1988 -- in front of the White House.

Clearing away the clutter and installing a pedestrian plaza would make the area more visitor-friendly and its appearance more historically appropriate, said landscape architect Michael Van Valkenburgh. The commission picked his Cambridge, Mass., firm last year to redesign the public space.

"The most important thing . . . was to restore a sense of dignity and pride for those of us who are outside the fence of the White House," Van Valkenburgh said.

He said his design would return a "sense of civicness" to the area for "the mom and dad with kids from Ohio or Massachusetts or the masses and protests. Those were the intents of what that street was designed for since the 1800s."

Congress has approved $6.1 million for the planning, design and certain structural tests before construction. In addition, $5 million was allocated to the Federal Highway Administration to look into the feasibility of building a tunnel under the part of Pennsylvania Avenue that runs in front of the White House and to address traffic problems resulting from street closures in the vicinity of the White House. President Bush's proposed 2004 budget includes $15 million to begin construction.

The Van Valkenburgh design is scheduled to go before the Commission of Fine Arts this month, and an environmental assessment by the Federal Highway Administration is to be released in April or May.

The plan is expected back before the National Capital Planning Commission in June and again, for final approval, in September, said commission spokeswoman Lisa McSpadden. She said the goal is to begin construction in November and to complete it by January 2005, in time for the presidential inaugural parade.