PORTLAND — Anti-tax activist Bill Sizemore is undaunted by seeing at least four of his five latest ballot measures rejected by Oregon voters.

He said he plans to file a 2010 measure to restore his double-majority requirement on local tax measures after it was limited by Measure 54, and threatened to sue political opponents he said waged a campaign characterizing him as a racketeer based on a civil judgment by a jury against his group, Oregon Taxpayers United.

“The next thing on my agenda is to get the final work done on a lawsuit suing the teachers union and their PACs and several individuals for libel and slander,’’ Sizemore said. “They have clearly crossed the line with some of their statements they said in some of their advertising.’’

And he held out hope for his top priority, the Measure 64 limit on the ability of public employee unions to collect union dues for political purposes. With 56 percent of ballots counted on Measure 64, the vote was 51 percent yes and 49 percent no. Many of the uncounted votes were in liberal Multnomah County.

“If I win on 64, it will be worth it all,’’ he said. “That’s the granddaddy of ballot measures. That’s the one they spent two-thirds of their money fighting.’’

Public employee unions spent more than $15 million on ballot measure campaigns, primarily fighting Sizemore’s measures. Sizemore’s work was financed by Loren Parks, the owner of a medical equipment company in Aloha who moved to Nevada in 2002.

“The real question is, is Oregon done with Sizemore? I think it is a resounding: Yes,’’ said Scott Moore of the Defend Oregon Coalition, a union-based organization that opposed all five measures put on the ballot by Sizemore and supported Measure 56, which eased the power of the double majority requirement on tax measures.

“It doesn’t matter to him what Oregon voters think. He’s shown repeatedly he will keep coming back again and again with the same stale ideas because this is what he gets paid to do.’’

Measure 56 limiting the double majority passed. It eliminates the need for a majority of registered voters to turn out in May and November elections in order for votes on local tax measures to count. Previously, only the general election in even-numbered years was exempt.

While it held down taxes, the rule hamstrung efforts by rural counties to balance their budgets as federal timber revenues disappeared, the result of national forest logging cutbacks to protect the spotted owl and salmon.

Reed College political science Prof. Paul Gronke said with so many measures on the ballot, a lot of Oregonians just voted no, as they did 66 percent to 44 percent against Measure 65, calling for open primaries.

“The voters of Oregon are getting tired of seeing 12, 15, 20 new ideas come on the ballot, some of which are half-baked, like this one,’’ he said.

Sizemore’s one purely tax-oriented measure, his third attempt to allow Oregonians to deduct all of their federal income taxes from their state income-tax returns, was rejected by voters. Measure 59 went down 63 percent to 37 percent.

“I think it’s always been clear that Oregonians are not interested in massive tax breaks to the wealthy,’’ said Moore. “The burden clearly would have been on the middle-class families.’’

Sizemore had attempted twice before to pass limitations on public employee unions, which he contends hold power over all three branches of state government. But opponents argued Measure 64 unfairly targeted government employees, and could hurt payroll contributions to charities.

Two other Sizemore measures proposing changes in the state school system failed. Measure 60 would have based teacher pay on classroom performance rather than seniority. Measure 58 would have required non-English speaking students to learn English within two years.

“I think Oregon voters trust the people who are closest to the classroom to make those decisions,’’ said Moore.

Sizemore’s Measure 63, exempting home improvement projects under $35,000 from requiring building permits, was rejected.

Former lawmaker and gubernatorial candidate Kevin Mannix’s proposed constitutional amendment to spend lottery money on crime labs and prosecutors went down. Measure 62 was defeated 59 percent to 44 percent after opponents voiced fears it could take money away from schools.

New mandatory criminal sentences remained unresolved. Measure 57 was a legislative referral to toughen sentences for drug dealers and thieves while expanding treatment programs. Measure 61 was another Mannix measure to require mandatory sentences for people convicted for the first time on nonviolent property and drug crimes. If both measures pass, the one with the most votes wins. With 57 percent of the vote counted, Measure 57 led by more than 100,000 votes.

Voters passed Measure 54, which lowers the age to vote in school board elections from 21 to 18.