A Massachusetts Institute of Technology scientist who showed that sodium nitrite causes cancer in rats says he agrees with the spirit of federal plans for a gradual phaseout of the antibotulism chemical from meat.

In a letter released by the Food and Drug Administration yesterday, Dr. Paul M. Newberne called FDA and Agriculture Department plans to start a phaseout as soon as possible "reasoned and rational."

Nitrite is widely used in processed meats like ham, bacon, sausage and lunch meat to retard bacterial growth and prevent deadly botulism.

It was Newberne's recent discovery about the chemical that last month prompted the FDA and USDA to start preparing a phaseout proposal. It is to be published in the Federal Register after a Justice Department review to make sure that it complies with the law.

In an Aug. 22 interview, Newberne told The Washington Post that his research definitely should be confirmed in other animals before any extensive ban, although, he said, there could be fairly quick action on some products. He said he agreed with FDA-USDA plans as long as a total ban on nitrite was regarded as a goal to be reached only if other safe preserving methods are perfected.

He said it might never be possible to remove nitrite from some products.

In his Aug. 25 letter to FDA Commissioner Dr. Donald Kennedy, Newberbe said "recent reports in the press have either misquoted me or have misinterpreted my comments."

He did not specify any misquotations, and he repeated much the same views that he had stated earlier. He told Kennedy that "the strongly suggestive nature of the results of the recent MIT study, and the established role of nitrite in the formation of nitrosamines" - other cancer-causing chemicals - "in my view leaves no responsible alternative except to attempt to substantially reduce nitrite as a food additive or, if feasible, to eventually eliminate it entirely."

He said he thought the initiation of a phasein of a ban need not await results of further animal studies, but that studies in other strains of rats and other species "should, however, be done concomitant to . . . a ban phasein."

FDA acting Associate Commissioner for Public Affairs Wayne Pines said yesterday he believes the FDA and Newberne are in agreement.He said eliminated over a period of years, but the FDA believes nitrite should be "our phaseout would be tied to the ability of industry to come up with alternative" antibotulism measures.

As to more animal studies of nitrite's effects - studies that might take three to four years - Pines said, "We will probably see the need for them, but there has been no firm decision."