Longtime supporters of Ronald Reagan are confident that the former California governor will stronly oppose the Panama Canal treaties proposed by President Carter.

"Frankly, the governor would lose standing with his national constituency" if he backed the treaties, a Reagan intimate said today, "Conservatives have a solid shot" at beating the treaties, and they "expect help from the man who made the Panama canal a big issue."

Two other prominent Republicans said they expected Reagan to make his opposition to the treaties known when he speaks Thursday nigh at the national convention of the Young Americans for Freedom in New York.

None of the Reagan supporters was willing to be quoted by name, however, since Reagan last week promised President Carter that he would make no public statement on the issue until he is briefed by treaty negotiators Ellsworth Bunker and Sol Linowitz.

Reagan associate Michael K. Deaver said that Reagan was sticking by what he said to the President when carter called him last week. Denver said Carter told Reagan that the proposed treaties, which guarantee U.S. access to the canal, met several of the objections Reagan raised in his 1976 presedential campaign.

"The governor does not plan to make any statement after the briefing in New York," Deaver said. He neither confirmed nor ruled out the possibility that Reagan would oppose the treaties in his Thursday evening speech , saying only that he plans to give a standard talk on "free enterprise."

Reagan's opposition to any new treaty was the spark that ignited his lagging presidential campaign during lagging presidential campaign during the North Carolina primary last year. He upset President Ford in that primary and subsequently came to the brink of winning the GOP presidential nomination.

Throughout the campaign. Reagan's battle cry on the Panama Canal that we bought it, we paid for it and it's ours" won loud ovations from Republican audiences.

But Reagan has made no statement since Carter announced the proposed treaties, partly because the President seized the political initiative by calling Reagan in an attempt to defuse potential opposition. Reagan's supporters and most other Repbulican politicals in California, also were thrown off stride by Sen. S.I. Hayakawa's (R-Calif.) tentative statement of support.

During his sucessful campaign for the Senate against Democratic incumbent John V. Tunney in 1976. Hayakawa won laughs by saying that the United States should keep the canal because "we stole it fair and square." After he was elected, however, Hayakawa responded to constituent letters on the issue by saying he favored continued negotiations to obtain a treaty.

Last week Hayakawa infuriated a number of his erstwhile conservative supporters by announcing support for the treaty package if it "looks as acceptable in particulars" as it did in the four-page summary issued by the White House.

In response, a memo sent out to 250 key Reagan backers urged a letter-writing and telephone campaign aimed at convincing Hayakawa to change his stand.

The memo was written on the letterhead of Citizens for the Republic, which Reagan heads. It was signed by Lyn Nofziger, executive vice chairman of the political action group and a veteran Reagan aide.

Deaver said that Reagan had telephone Hayakawa this morning, after a story on the memo appeared in the Los Angeles Times to assure him that he was not the author of it. Reagan reiterated his position that he would wait until his briefing by the treaty negotiators to arrive at a position Deaver said.

But the memo was regarded by most California Republican leaders as a sure sign of the direction in which Reagan is heading.

"Hayakawa needs to know that California Republicans oppose the proposed canal treaty," the Nofzeger memo said. "Please send him your protest without delay."

With Hayakawa on one side and Reagan probably on the other the canal issue promises to divide Republicans here this year as much as it did in 1976.

Both Reagan and Ford, who has announced his support for the treaties have been invited to speak at the GOP convention in California in San Diego Sept. 30-Oct. 2.

One GOP official with responsibility ties for the meeting said that the two former presidential candidates will speak on different nights and that an effort is being made to have them address any issue other than the Panama Canal.