LOS ANGELES, OCT. 23 -- Democratic leaders of the California legislature today unveiled their secret weapon in a last-minute attempt to stop a movement to limit the terms of politicians.

To soothe frustrated voters who say they want to throw all political veterans out of the state capital in Sacramento, Assembly Speaker Willie Brown (D) and other leaders called on one of the nation's most trusted television personas, actress Angela Lansbury, to steer voters politely from what she called "the term-limit trap."

Lansbury, best known for her role as a crime-solving mystery writer in the television series "Murder, She Wrote," leans earnestly toward the camera in a 30-second television commercial that began broadcasting today and says if two term-limiting initiatives on the Nov. 6 ballot are approved, "special-interest groups and developers will amass even more power -- and millions of your tax dollars will go to politicians' campaigns."

The campaign against propositions 131 and 140 has only two weeks to derail initiatives that showed as much as 3 to 1 support in the latest Mervin Field California Poll. The spot's producers, political consultants Michael Berman and Carl D'Agostino, successfully killed two redistricting initiatives in June with similar commercials using actors Jack Lemmon and James Garner, and they appear to have more money than the initiatives' supporters.

Proposition 140, favored 68 to 20 percent in the California Poll, would impose a lifetime limit of six years in office on state Assembly members and eight years on state senators and most statewide elected officials, as well as cut legislators' expenses and kill their pension plan. Proposition 131, favored by 52 to 29 percent, would limit state legislators to 12 consecutive years in office and most statewide officers to eight years, as well as limit special-interest campaign contributions and provide some public campaign financing. Term limits have passed in Oklahoma, are on the Colorado ballot and are being considered in other states.

J.G. Ford Jr., president of the Marin United Taxpayers Association and a principal sponsor of Proposition 140, said he thought "only a small minority would be suckered in" by the Lansbury ad. But he acknowledged that his campaign had only $500,000, enough for radio but not television advertisements, and was concerned about Berman and D'Agostino's skill at reaching voters. Field has said his poll measured only initial impressions of the initiatives, which could change.

Campaign officials indicated that Lansbury's warm television performances have obliterated memory of her dark role in the 1963 film, "The Manchurian Candidate," in which she played a vice presidential candidate's wife trying to arrange through brainwashing and assassination a communist takeover of the United States.

She briskly begins the new television spot by saying: "Sponsors of 131 and 140 call them term-limit reforms. But these so-called reforms are written by politicians. They're using term limits as a come-on to get your vote. Read the fine print!" Campaign spokesman Jay Ziegler said "one or two" other spots also are being prepared but said estimates of a $4 million opposition campaign fund were inflated.

Yes-on-131 campaign manager Jim Wheaton characterized the spot as "scared politicians hiding behind a Hollywood actor" and said it violated state law by failing to identify Speaker Brown and other sponsors. Ziegler released a legal opinion saying identification was not required of a campaign fighting two initiatives at once.