Kaczynski and his wife, Maria Kaczynska, were among 96 peoplein western Russia. Investigators are as the cause.
Mourners knelt, prayed and cried before the first couple's coffins in the Columned Hall of the palace, where the president appointed and dismissed governments. The line to get in swelled to over half a mile.
"We will wait as long as it takes," said Alicja Marszalek, a retired telephone operator who was waiting with a friend. "We want to pay homage to them because they were wonderful people. He was a modest man, very well educated, intelligent and kind."
Polish television broadcast live images of mourners walking by the closed coffins. Many were families with children, parents and grandparents. A pair of soldiers flanked each coffin, standing crisp and still.
Earlier Tuesday, Kaczynska's body was greeted with tears and tulips after being flown home from Russia. Officials announced that the first couple would be buried Sunday after a state funeral at Krakow's Wawel Cathedral.
Krakow Archbishop Stanislaw Dziwisz said the funeral would begin at 2 p.m. local time (7 a.m. Eastern time) Sunday in the 1,000-year-old cathedral - the main burial site of Polish monarchs since the 14th century and more recent heroes including the 20th century Polish statesman and military leader Jozef Pilsudski.
The last Polish leader killed in office, Gen. Wladyslaw Sikorski - the exiled World War II leader who perished in a mysterious plane crash off Gibraltar in 1943 - is also interred there.
Some Poles criticized the decision to bury Kaczynski, whose combative style earned him many opponents, in a place reserved for the most esteemed of national figures. Hundreds staged a protest in front of the archbishop's residence in Krakow on Tuesday evening, carrying banners reading "Really worthy of kings?" and "Not to Wawel."
In Washington, the White House announced that President Obama would. Russia President Russian President Dmitri Medvedev and French President Nicolas Sarkozy are also expected to attend.
Kaczynska's body, in a wooden casket draped with Poland's white-and-red flag, arrived in a military CASA plane at Warsaw's Okecie airport. It was met by her only child, Marta, and by Jaroslaw Kaczynski, her brother-in-law, the twin of the late president.
Marta knelt by her mother's casket and wept as an honor guard stood by.
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Poland's President Killed in Plane Crash
Kaczynska's body was ferried slowly to the Presidential Palace in a black Mercedes-Benz hearse, as her husband's had been on Sunday. Thousands of Warsaw residents lined the route, gently lobbing bouquets of tulips and roses on top of the hearse.
"I'm here because it's such a tragedy for Poland," said Maja Jelenicka, 63. "I'm in despair. I feel as if I've lost a close relative. Maria Kaczynska was a wonderful woman, kind, with a heart of gold."
Parliament held an observance in memory of the president and the 18 lawmakers killed in the crash. In the assembly hall, framed portraits of the lawmakers and flowers bedecked their empty seats.
The names of the victims were read out. Senate Speaker Bogdan Borusewicz, his voice breaking, declared the crash the "greatest tragedy in Poland's postwar history."
Investigators have suggested that human error may have been to blame for Saturday's crash. The Tu-154 went down while trying to land in dense fog at Smolensk in western Russia. All aboard were killed, including dozens of Polish political, military and religious leaders.
They had been traveling in the Polish government-owned plane to attend a memorial in the Katyn forest for thousands of Polish military officers executed 70 years ago by Josef Stalin's secret police.
Russian Deputy Prime Minister Sergei Ivanov said Tuesday the plane appeared to have been functioning normally.
"Judging by preliminary analysis of data from the black boxes, there was no explosion or fire aboard the plane, and the engines were working until the collision," Ivanov said in televised remarks.
The pilot had been warned of bad weather in Smolensk and advised by traffic controllers to land elsewhere - which would have delayed the Katyn observances. He was identified as Capt. Arkadiusz Protasiuk, 36; the co-pilot was Maj. Robert Grzywna, also 36.
Traffic controller Anatoly Muravyev, a member of the Russian team that handled the plane, told the Komsomolskaya Pravda newspaper that the crew ignored their warnings about worsening weather.
The crew "started landing with confidence and with no swerving," Muravyev was quoted as saying. "But then the traffic controllers had doubts."
He said the head controller three times ordered the plane to reattempt the landing and then advised the pilot to fly to another airport.
"The crew did not listen, although the controllers warned them about bad visibility and told them to get ready to fly to a reserve airport," Muravyev said.
Polish Prosecutor General Andrzej Seremet said Polish prosecutors were still reviewing data from the flight recorders and would discuss their findings Thursday.
So far, 87 bodies have been recovered and 40 of them identified, he said.