The grass was supposed to be planted by now on the closed part of Pennsylvania Avenue in front of the White House, but the Clinton administration said yesterday that a series of glitches with contractors and last week's federal government shutdown had delayed the beautification effort until at least December.

Even before the temporary plan to spruce up the street gets underway, though, a panel of 14 nationally known architects, planners and historical preservation specialists will meet here the week of Dec. 11 to propose a permanent design for the two-block area.

"We were probably more hopeful" in the schedule for the interim work, conceded James I. McDaniel, the National Park Service's White House liaison. "Once you get into the process of procurement and contracting there are always little complicated details you have to work out."

In May, Clinton ordered Pennsylvania Avenue closed between 15th and 17th streets NW because of security concerns after the Oklahoma City bombing. Under the $1 million temporary plan announced two months ago, much of the street's asphalt in front of the White House will be torn up and replaced with 40-foot-wide strips of grass. The idea is to soften the view from either end of the avenue.

In addition, the makeshift concrete planters and barriers blocking off Pennsylvania at 15th and 17th streets NW will be taken away. In their place will be more attractive square and circular planters.

Gone too will be most of the parked police cars that now restrict access to the street, replaced by guard booths and movable steel barricades that will allow authorized vehicles to pass.

McDaniel said the grassy strips probably will not be completed until sometime in the spring, in part because trolley tracks have been discovered during excavation. A decision still must be made whether to save them for a future line on these two blocks or to work around them.

The beige planters are being made by a Georgia company, and the first delivery should be in about two weeks, he said. The guard booths, financed by the Secret Service, should be in place within eight weeks. The government is trying to persuade the American Association of Nurserymen to donate magnolia trees, roses and other plantings.

"The planters will be the first physical sign of change," McDaniel said.

Officials also are considering ways to reopen E Street to traffic in both directions. It is now one way eastbound.

The interim plan is supposed to be in place for about two years.

A final design will be chosen in January 1997, from the list of proposals made next month by the panel of architects and preservation specialists.

The public has submitted about 100 ideas to the Park Service, some of which may be included in the panel's proposals. A class of architecture students at the University of the District of Columbia suggested, among other things, that an interactive area be built along the street where historical figures would "speak" to visitors.

Sarah C. Dawson, of Arlington, and her son, Forrest, described an area called "Peace Paths" where the names of Nobel Peace Prize winners would be etched in a flagstone walkway.

"The idea," she said yesterday, "is to promote some serenity and peace and contemplation because that street was closed off due to violence."