Irena Sendler, 98, a Holocaust heroine

Irena Sendler, 98, a Polish Catholic social worker who helped lead a smuggling operation that rescued thousands of children from Warsaw's Jewish ghetto during World War II, died Monday at a Warsaw hospital. She had pneumonia.

After the German invasion of Poland in 1939, an estimated 400,000 Jews were forced into the ghetto, the size of 16 city blocks. They faced disease, execution, or deportation to concentration camps, and the hopelessness led to a ghetto revolt in early 1943 that ended in a slaughter by the Nazis.

Ms. Sendler, aiding Jews since the start of the war, became an early activist in the clandestine group Zegota. The underground movement - whose members faced execution if caught - formed in 1942 after the deportation of 280,000 of Warsaw's Jews to the Treblinka death camp.

Ms. Sendler used her senior position with the city's welfare department to win access to and from the ghetto and set up a network of 25 associates to help organize escapes and falsify documents.

Under the code name Jolanta, she became one of Zegota's most successful workers. She eventually took charge of the Zegota children's division and helped spirit the children out of the ghetto in ambulances by hiding them under blankets, in burlap sacks and toolboxes, and sometimes in coffins.

To distract German guards, she kept a barking dog on the front seat of her ambulance to drown out the cries of young children who feared separation from their parents.

Ms. Sendler used her contacts at orphanages and convents to keep Jewish children safe until the war's end, often under Christianized names.

The intention was to return all the children to their parents, although the death rate of the adult population made the task largely impossible. But for years Ms. Sendler guarded the real names of the children and their parents, writing them on tissue paper and burying the lists in jars under an apple tree at an associate's home.

On Oct. 20, 1943, the Gestapo arrested her and took her to Pawiak prison, where subversives were tortured and killed. For three months, her captors used clubs and other devices to fracture her legs and feet.

She did not inform on Zegota leaders and was sentenced to death by firing squad, but a bribed guard helped her escape and marked her as having been executed. Ms. Sendler remained incognito for the rest of the war and continued to help Zegota.