I’ll preface this by saying that this is not a specialty of mine, and add that even as far as nuclear programs go the Israeli nuclear program is arguably the most secretive in world history except maybe for South Africa.

But: I have never come across any suggestion that it is “generally accepted that the U.S. covertly supplied Israel with nuclear weapons...”

That’s the plot of the film (and book? I haven’t read it) The Sum of All Fears. But I’m not aware of it actually happening. The much more relevant international partnership in the Israeli construction of nuclear weapons was French assistance in building Dimona.

After they had a working, independent, un-inspected nuclear reactor, the Israelis didn’t really need a US “sale” to build a bomb. They built it themselves.

As far as I’m aware, US knowledge of and potential cooperation with Israel’s nuclear program remains one of the most sensitive of classified subjects. There was an incident a few years ago when an American nuclear researcher was fired for apparently “revealing” that Israel has nukes in an article: https://www.publicintegrity.org/2014/07/31/15161/nuclear-weapons-lab-employee-fired-after-publishing-scathing-critique-arms-race

So I wouldn’t expect anything more concrete to frankly ever become available.

If you have information to the contrary about a US “sale” I would love to see it.

Also worth noting is that this is of course to say nothing about US sales and military aid to Israel of conventional arms, which has been enormous.

The United States never sold or supplied Israel with nuclear weapons. In fact, like South Korea, it sought to prevent Israel from gaining nuclear weapons. It simply failed in that quest.

You can read more about it in Israel and the Bomb by Avner Cohen, considered one of the better scholars on Israel's secret program's history. Kennedy was extremely engaged in trying to get Israel to accept IAEA inspections and tighter controls on its nuclear program to prevent weapons development. Americans were allowed to tour the facility at least twice, but Israel is believed to have prepared the facility to hide its ultimate goal, and generally used the trips to relieve American diplomatic pressure and put the US at ease.

When Israel purchased yellowcake from the Argentinians, the US put pressure on the Argentinians to enhance restrictions on sale, the Israelis refused to answer questions about the purchase when the US tried to quiz them on a visit in 1966 to Dimona, and the US generally tried to stop the sale itself but failed miserably to even learn much about it quickly (and they quickly found it was irreversible by that point).

The US even considered confronting Israel after it was believed they had a bomb, which was believed to have been all but assembled (that was the last stage, they figured) by 1968-69. In response, the US issued memoranda discussing potential ways of dealing with the question of an Israeli bomb (which had come into being relatively quickly, less than 10 years, after the revelation of a potential nuclear program in Israel), and a Senior Review Group put together proposals for Nixon. The SRG recommended repeatedly seeking to get Israel to ratify the NPT, and to agree not to introduce nuclear weapons or deploy them, as well as an agreement not to move forward on building them. A strategy document believed to have been drafted or at least heavily influenced by Kissinger in 1969 that stated that the goal of "what we want" was best defined as for Israel to "Not assemble completed nuclear explosive devices", and the paper suggested that the only realistic goal that they could "really want" was to simply get Israel not to publicize its nuclear weapons, since it was probably all they could achieve. The paper also said that signing the NPT should be the "absolute minimum". In short, the US realized it was unlikely to be able to reverse the nuclear program, and instead sought to minimize potential diplomatic issues as a result of the revelation of nuclear weapons possession by Israel, as well as to minimize completion of nuclear explosive devices in the future.

The US definitely did not complete a "potentially-incredibly-damaging arms sale" of nuclear weapons to Israel as far as we know, and it did pressure Israel to not seek nuclear weapons. However, Israel's level of secrecy on the subject, its ability to fool inspections, and the lack of overall focus on it because of the variety of other foreign policy crises ongoing (Cuban Missile Crisis, war between India and China, etc.) led to less focus.

Additionally, the US had far more leverage over South Korea than Israel. In the 1960s, Israel was not strongly supported by or reliant on the United States. Until 1966-67, its main arms supplier was France, not the US, and the US was not a main supplier of aid. Indeed, aid did not get regularized and increase until the Nixon presidency, by which point nuclear weapons were already effectively in Israel's hands, or about to be. South Korea, on the other hand, considered nuclear weapons as a result of the US consideration of withdrawing forces from the Korean Peninsula. The US had significant leverage over South Korea and France, which was considering helping South Korea with a nuclear reprocessing facility, whereas with Israel, France provided the assistance covertly. Furthermore, South Korea had a nuclear umbrella provided by the US, making it easier to influence them through nuclear guarantee.