Award of the massive and exuberant crowds that Pope Paul II has drawn in Boston, New York and Philadelphia, officials here are preparing for an unprecedented outpouring of up to 1 million worshipers in Washington tomorrow and Sunday.

Planners rushed through last-minute preparations yesterday, lining up extra buses and subway trains, stocking up medical emergency supplies and food, and installing extra radios and telephones for quick communication.

Final details of traffic control were being worked out by police in anticipation of massive traffic jams. Many streets in the Mall area will be closed Sunday and parking will be restricted elsewhere.

Transportation, medical, food service and sanitation systems are expected to be taxed to their limit and beyond, especially on the Mall, where the pope will celebrate a huge open-air mass on Sunday.

"We're planning for 1 million people," said William H. Rumsey, head of the mayor's special events task force. "We'd rather have it and not need it (large-scale logistical support) than need it and not have it."

Officials said they expect delays and breakdowns with such large crowds. They urged worshipers to be patient, come early, bring a picnic basket, expect to stay late and not drive near the Mall.

The weather outlook is a mixed bag, National Weather Service forecasters call for partly cloudy conditions tomorrow with little or no chance of rain. But on Sunday, the day of the mass on the Mall, there is a 30- to 50-percent chance of showers.

Temperatures are expected to take a somewhat chilly turn, with lows in the 40s and low 50s at night and highs reaching only the mid-60s during the day.

There were signs yesterday that some of the thousands expected here are already on their way. Charter buses from as far away as Florida and Louisiana have begun the two-day journey.Other out-of-towners are arriving today, some to stay in hotels, others to bed down in area homes.

Washington hotel managers were expecting no serious shortage of hotel space during the pope's weekend visit, primarily because weekend sales are traditionally slow. But spokesmen for the hotel associations said the pope's visit would probably increase weekend occupancy from the customary 50 percent to 80 or 90 percent.

Restaurant owners and retail shopping managers also were not planning for overcapacity crowds. "I think they (merchants) look at it as the religious pilgrimage that it is and are kind of pleased that Washington is included," said Austin G. Kenny, director of the conventions and visitors bureau.

However, charter bus and Tourmobile officials were expecting overflow business that would give them a boost after last summer's lagging tourist season.

Besides the papal mass on the Mall beginning at 3 p.m. Sunday, there will be other opportunities to see the pontiff during his two-day visit.

There will be three parades through downtown streets tomorrow, plus a flurry of activity at Catholic University and the National Shrine of the Immaculate Conception in Northeast Washington Sunday morning.

After flying in to Andrews Air Force Base from Chicago tomorrow, the pope will be ferried into the city by helicopter. He will arrive at 11 a.m. at the Rainbow Pool near the eastern end of the Reflecting Pool at 17th Street and the Washington Monument grounds.

There, he will be greated by a special assemblage of Catholic school children, and Mayor Marion Barry will present him the keys to the city.

The pope and his entourage will then parade up 17th and K Streets to St. Matthew's Cathedral in the 1700 block of Rhode Island Avenue NW. For this and other parades, the pontiff is expected to ride in an open Secret Service limousine and wave to the crowds along the way.

After a special mass and a luncheon at St. Matthews's, the pope will parade down Connecticut Avenue and 17th Street to the White House around 1:30 p.m. for a meeting with President Carter and other officials.

The pope's third and last parade of the day will come at about 4:30 p.m., when he goes from the White House down 17th Street to the nearby Pan American Union building for a reception by the Organization of American States.

The pope will stay overnight at the apostolic delegation residence, 3339 Massachusetts Ave. NW near the Naval Observatory.

Early Sunday, he will be driven to Northeast Washington for various meetings and prayer services at the Shrine of the Immaculate Conception, the Catholic University field house and the chapel at Trinity College.

Viewers will be able to catch glimpses of the pope as he arrives at the Shrine at about 8:05 a.m. to address 4,000 nuns and again at 9:15 a.m. when he emerges from the Shrine and parades briefly on Michigan Avenue to the Catholic University field house for a meeting with theologians and other academics.

At 10:20 a.m., he will parade again on Michigan Avenue from the field house to nearby Trinity College for an ecumenical meeting with representatives of several non-Catholic Christian churches.

About an hour later, the pope will leave Trinity, returning by "closed motorcade" -- not a parade -- to the apostolic delegation to rest before going to the Mall for the scheduled 3 p.m. mass there.

He will make a final parade about 2:30 p.m. as he enters the Mall area for the mass, moving along Constitution Avenue from 17th to 3d streets NW.

During the mass, the pope will be visible to worshipers as he stands on the specially constructed three-tiered stage just in front of the Smithsonian Castle on the Mall. An elaborate sound system with speakers mounted on five 60-foot towers along the Mall will project the pope's voice from at least 4th to 14th Street, planners said.

After the mass, the pontiff will return to the apostolic delegation, fly by helicopter to Andrews Air Force Base and depart for Rome Sunday night.

Police and transportation planners expect major traffic jams as the crowds break up Sunday evening on the Mall.

Metro's subway trains will carry large portions of the crowd away. Police say they will close station entrances periodically if overcrowding occurs. Many people will take shuttle buses back to fringe parking. Many others will walk.

Police from several jurisdictions will coordinate traffic on outbound arteries from the city. The southbound span of the 14th Street Bridge will be opened for pedestrians only, as police anticipate that thousands of worshipers who came from points south of Washington will walk back to their chartered buses at the Pentagon parking lots. Other mass-goers are expected to walk to bus and car parking lots at RFK Stadium.

Church officials cautioned that the pope's schedule there, including parade time, is approximate and subject to delays.The pope has periodically run behind schedule in other cities he has visited this week.