Just as the script came to the part about Alexandria's "delicately balanced urban renewal program," the slide projector flashed a picture of a humongous rubble of twisted metal and brick. The audience of 10 crowded into a tiny Alexandria city office dissolved in laughter.

"That's not exactly what we meant," someone said wryly. "Maybe just take out the word 'delicately'?" another watcher suggested.

It was rehearsal time. All this week, Alexandria city officials and residents have been practicing the audio-visual presentation they will give Monday at the National Conference on Government in San Antonio when they compete with 16 other localities (one of them, Pocomoke City, is on Maryland's lower Eastern Shore) for the All-America City award.

Each city has 10 minutes to state its case before a jury of six. A bell will cut off verbal meanderers.

"My nightmare is that we might end up like Ronald Reagan, you know, talking about driving down the Pacific Coast and getting cut off," said Vola Lawson, Alexandria's assistant city manager for housing, who is overseeing the project.

Lawson's word-whittling cut the delivery time of Alexandria's script from 17 minutes to 8 1/2. However, the narrator had to speak at such breakneck speed to keep pace with the slides that a slide-winnowing process was ordered.

City manager Doug Harmon vetoed a slide of a headless naked female sculpture to illustrate local artists' efforts to restore the Torpedo Factory. "You can't tell if that's an artist's work or a city official," he joked.

Mayor Charles E. Beatley, Vice Mayor Patricia S. Ticer, City Council members Lionel Hope and Robert L. Calhoun and city manager Harmon are departing Saturday for San Antonio. Del. Marion Van Landingham (D-Alexandria) will join the delegation there along with citizens responsible for the three projects that Alexandria is highlighting as its success stories:

* "Friends of Alexandria Public Schools," an effort launched in 1982 by Judy Harmon, wife of the city manager, and Judy Seltz to counter bad publicity they believed real estate agents in the area were giving the city's school system.

* MICAH Housing Inc., a program that used federal funds to allow low-income residents to buy, rehabilitate and manage the Fayette Court apartments. Mary Ellen Bayer, MICAH founding president, and Ora Edmond, president of the residents' council, will represent the project.

* The $2 million refurbishing of the waterfront Torpedo Factory by a group of local artists, which Van Landingham will represent.

This year's 17 finalists for All-America City, chosen from 100 entries, range from Dallas to the Eastern Shore hamlet of Pocomoke City, Md.

Last Monday, Pocomoke City Manager Russell Blake answered the phone at City Hall. Despite the holiday he and his San Antonio delegation were rehearsing.

Merely being selected as a finalist "for a town as small as we are has generated a lot of civic pride," said Blake, pointing out that the three projects they will showcase involve "2 percent of our population." That's 2 percent of 3,600 people.

An All-America City award, which Alexandria won in 1964, brings no monetary gain. "The only tangible thing they get is a flag at an award ceremony," said Joan Casey, director of publications at the New York office of the sponsoring organization, the Citizens Forum on Self-Government, formerly the National Municipal League.

"Pride" is the primary motivator for seeking the honor, she said.

Criteria for the award, given out yearly since 1949, are that the projects result from citizens' efforts and that they address community problems, said Marion Kelly, administrator of the program.

After Monday's presentations, the jury will choose about half of the competitors as potential award winners. The forum then will send representatives unannounced to each city to verify the stories. Winners will be announced next spring.

Past winners in the area have included Baltimore, in 1976 and 1952; Falls Church, in 1961, and Rockville, which has won the award four times, most recently in 1978. The District has never entered the contest, Kelly said.