"Testing, testing . . . ," boomed the voice across the nearly empty Mall yesterday from the huge 60-foot sound tower. "There's much more muffin the middle of an egg than egg in the middle of a muffin."

The funbled commercial jingle echoed off the granite buildings as technicians made last-minute adjustments on the sound system that Pope John Paul II will use this afternoon when he celebrates mass for up to 1 million worshipers.

Not only sound technicians but carpenters, painters, electricians and other workers scurried throughout the day to put the finishing touches on the massive stage and altar for the outdoor mass scheduled for 3 p.m. today.

The air filled with the whine of buzz saws and the tap-tap of hammers as workmen hastily constructed a platform for news photographers. Electricians sorted through hundres of multicolored wires that snaked across the ground and disappeared into a manhole. Volunteer workers carefully rearranged some of the thousands of chrysanthemums around the stage.

Above it all, the 22-foot high wooden backdrop for the papal altar and chair glistened with frest white paint.

Scores of squatters -- mostly college and high school kids seeking a close view of the pontiff -- were camped along the chain link fence surrounding the stage and altar in front of the Smithsonian Castle. They played cards, traded books and newspapers and ate peanut butter sandwiches to while away the hours.

As the day wore on, activity at the stage and altar attracted thousands of curiosity seekers. Lectors practiced scriptural passages over the loudspeaker system while others read a series of intercessions in a variety of foreign languages.

In the afternoon, four Caribbean-style bands from the American Folk-life Festival circled the Mall on Flatbed trucks, beating out their throbbing reggae rhythms.

In sharp contrast, choral director Paul Traver led a 500-voice primary choir through its final rehearsal for the mass today, as it sang liturgical music. The choir was accompanied by an organ and brass and woodwind ensemble.

Everyone from the squatters, singers and workmen on the Mall to police officials, hotel clerks and transportation coordinators who were scattered across town toiled to meet their various deadlines for today.

Policy and transportation officials put the final touches on extraordinary plans to deal with the expected crowds. However, none of them knew exactly how many people to expect and exactly what their problems might be.

The big barricade for automobile drivers will be the Mall area, which will be closed to vehicular traffic throughout the day from 3rd Street to 23rd Street NW and from Independence Avenue to Pennsylvania Avenue or E Street NW. Northbound and southbound tunnels under the Mall will be kept open most of the day, however, officials said.

Hotel desks around the area reported business heavier than usual for a Saturday and many downtown hotels were beginning to fill up. Rooms were still available yesterday evening, however, inside the Capital Beltway.

The uncertainty of the crowd size was the haunting factor for Metro officials. "If there are really one million people out there and a major number of them use us," a senior Metro officials said, "it could take us four to five hours to clear the Mall after the mass." The mass is scheduled to end at 5:30 p.m., with choirs singing for some time after that.

Final assignments were checked yesterday for police and other personnel to limit the number of people who will be permitted into a Metro station at any one time to prevent overcrowding on the platforms.

Archdiocesan officials told Park Police and Metro that they expect a minimum of 3,000 chartered buses -- about 150,000 people -- and could get as many as 6,000 chartered buses.

The chartered buses will be parked in fringe lots at the Pentagon and in East and West Potomac parks and RFK Stadium. Shuttle buses operated by Metrobus or Tourmobile will carry patrons from the parking lots to the Mall and back again.

A total of 250 barrels were rolled up to the various Metro entrances so passengers could toss their fares into them instead of having to deal with the unpredictable Farecard machines. Additionall, each station attendant was issued a bucket of water to put out a fire in the barrels in the event somebody tosses in a cigarette, igniting paper money.

Area police forces reported they are scheduling extra shifts to handle traffic and crowd problems. Virginia State Police shifted personnel from other areas of the state to beef up patrols along Shirley Highway and the Beltway.

The hotel industry usually does not expect to make money on the weekends in Washington, but things looked better than usual yesterday. Gail Zamore at the Holiday Inn, 1900 Connecticut Ave. NW, said that the majority of Holiday Inn rooms in the area were booked. But, she said, "some people are checking out because they tell us they want to avoid the crowds with the pope tomorrow."

At the swank Hay-Adams, immediately across Lafayette Square from the White House, the desk clerk reported all rooms booked and said many of the guests were there to attend the White House reception for the pope.

"It's like a carnival atmosphere around here," he said. "I've never seen anything like it in this hotel."

Nonetheless, calls to seven other hotels or motels in the area showed that rooms were still available last night.

Transportation, police and hotel probelms were not the only logistical concerns in the area. Jim Highsmith of Coca-Cola was busy setting up concession stands on the Mall yesterday.

He said that Coca-Cola will preposition about 2,000 tanks of "Coke premix" at locations around the Mall. Each tank, when emptied into 7-ounce glasses containing 3 ounces of ice, will serve about 125 people. "We've got four locations in the area for resupply if we need it," Highsmith said.

At the Mall, construction supervisors expressed confidence that all will be ready for the mass today.

Shortly after noon yesterday, a massive red oak altar was lowered onto the three-tiered papal stage by crane and secured. It will be at this altar, whose top measures 4 feet by 11 feet, that the pope will consecrete the hosts for the hundreds of thousands of worshipers expected to take communion. About 1,500 priests and deacons will fan out into the crowd to offer the communion wafers.

The pope is scheduled to arrive in the Mall area around 2:30 p.m. waving to the crowds from an open limousine as he travels east on Constitution Avenue NW from 17th to 3rd streets. At 3rd, he will turn south across the Mall to Jefferson Drive, then go west along Jefferson to the Smithsonian Castle.

If the schedule holds, the mass should begin at 3 p.m., with the pope leading a procession through an assemblage of 4,000 church officials, special communicants and other VIPs in the fence-enclosed area around the stage and altar.

The pope's voice will be amplified by an elaborate network of speakers mounted on four 50- to 60-foot sound towers placed along the Mall from 7th to 14th streets.

As engineers tested the sound system yesterday, one many began reading from a technical manual. Phrases such as "interfacing with the oscilloscope" and "analogue to the digital converter" resounded across the Mall.

After several minutes, the man suddenly stopped and said, "I'm tired of reading this stuff."