hat tip to reader SF who corrected me.

 Reagan was no longer governor in 1978 when Proposition 13 was passed. He was devoting his time to winning the nomination for president.

I just had just seen Milk Thursday night, and was struck by the fact that Proposition 13 and Proposition 6 were then on the ballot. I was struck by the fact that Reagan opposed proposition 6 which would have prevented gays from teaching in Califronia schools and I assumed that he was still governor.

An article in The American Spectator, Reagan and Milk has an interesting discussion on Reagan's motives for opposing the bill. He agreed to support the opposition led by Milk when it was pointed out to him that it would be government interference in personal matters and could lead to victimization of straight teacher by students and parents who bore grudges against them for other reasons.

Reagan did begin the process that led to the passage of the Jarvis proposition 13, with his support to proposition 1, which was defeated. There is an interesting article on this in a review of a 2003 book by Reagan biographer, Lou Cannon. Here's the relevant excerpt: from his biography of Reagan, Governor Reagan, His Rise to Power,

An exception to Cannon's assessment that Reagan was an astute and pragmatic politician is his judgment that Reagan's support of Proposition 1 was a mistake, indeed a fiasco. Proposition 1 was a complicated ballot initiative to amend the California Constitution to accomplish the dual purposes of (a) limiting state taxes and state spending to the 1973 level of spending in relation to personal income (8.3 percent), and then (b) to reduce this to 7.0 percent over a number of years. It was defeated 54-46 percent in November 1973. The Los Angeles Times opined that Reagan had lost his first major election in California and wasn't even on the ballot. According to Cannon, it was "a resounding and unnecessary defeat" brought about by the failure of Reagan's aides to advise him properly on political risks. But Reagan had called Proposition 1 "a oncein- a-lifetime opportunity." Taxpayer revolt would gain greater steam in the late 1970s with Proposition 13 (passed June 1978), supported by Reagan and considered the opening wedge in a national trend of tax limitation. Proposition 13 limited only property taxes; Reagan sought with Proposition 1 to limit overall state taxing and spending. Proposition 1 would have had a better chance had it simply capped, rather than trying to roll back, state spending and taxing.

Nevertheless, one wonders whether Proposition 1 was not an inevitable and essential part of the Reagan saga. When he took office, Reagan dealt with the existing imbalance of the California budget by raising taxes; later legislation provided some tax relief, but California taxes and spending were greater in relation to state personal income at the end of his tenure than at the start. With Proposition 1, Reagan tried to limit and eventually reduce the state's tax and spending burden. It thus foreshadowed not only Reagan's support for California's Prop 13 but his support as president for the national balanced budget and tax limitation amendment.

The signature tax initiative of Reagan's presidency was his initial, across-the-board income tax cuts. Domestic spending control was more difficult, and Reagan did not get all the spending reductions for which he asked—either in 1981 or in later years. In 1982, the proposed constitutional amendment to limit taxes and balance the budget passed the Senate but failed in the House. "I think we have learned," he wrote R. Emmett Tyrrell, editor of the American Spectator, in 1983, "that government's wants are limitless." Although domestic spending was reduced during Reagan's presidency by 1.5 percentage points of GDP, it increased to its old levels and beyond during the Bush and Clinton eras. Reagan's support of Proposition 1, like his support of the constitutional amendment in 1982, expressed his fundamental belief in the importance of external limits on taxes and spending.