State Sen. Leland Yee, D-San Francisco, announced Monday that he will not run for U.S. Rep. Tom Lantos' seat in Congress.

"I am humbled by the outpouring of support from the people of San Francisco and San Mateo County who have encouraged me to run for Congress," Yee said in a statement. "However, at this time, my family and I have decided it is best to continue the work started in the state Senate."

Yee, 59, had been considering a run after news came that Lantos, D-San Mateo, has cancer of the esophagus and will not seek a 15th term this fall. Yee was seen as a potentially serious Democratic primary opponent for state Sen. Jackie Speier, who launched her campaign Sunday.

Elected to the state Senate in 2006, Yee said he wants to focus on unfinished business there, especially the effort to provide universal health care for the state.

Political observers had noted that Yee could have run for Lantos' seat without giving up his post in the state Senate. On Monday, San Jose State University political science professor Larry Gerston said Yee's decision not to run speaks to Speier's strength as a candidate.

"There's no reason to tilt at windmills," Gerston said. "Speier has a tremendous amount of support. And you can't dismiss the emotional element" that stems from her association with former U.S. Rep. Leo Ryan, who held the same congressional seat before being shot dead in Guyana, after his 1978 visit to Jonestown.

"For people in that generation, there's kind of a closing of the loop here 29 years later," Gerston said. "I think it helps to