The Senate Agriculture Committee took steps yesterday virtually assuring that new farm law will contain some of the strongest soil-conservation provisions in years, voting to ban federal aid to farmers who cultivate highly erodible land.

As its House counterpart did earlier this week, the Senate committee went well beyond Agriculture Secretary John R. Block's recent proposal that as much as 20 million acres be devoted to a conservation reserve to protect the environment and reduce surplus crop production.

The panel voted to set up a long-term reserve of up to 30 million acres -- 5 million more than in the House version -- by paying farmers to remove their most erosive land from production. Agriculture Department officials estimate that as much as 53 million acres of cropland could qualify for the reserve immediately.

The Senate panel also went beyond its House counterpart by proposing to ban all federal farm program assistance to any farmer who continues to cultivate highly erosive land after 1988 without a government-approved conservation plan.

Although the legislation would not prohibit farming on highly erosive lands, some House committee members denounced the ban on aid as "confiscatory" and "draconian."

"We're only precluding these people from receiving federal benefits," Sen. Rudy Boschwitz (R-Minn.) said yesterday. "It is important to me that we do not continue to pay people who plowed up highly erodible land . . . . A lot of land has been put into production because of the farm programs we have had. This bill should take a very firm stand."

The ban on benefits payments after 1988 was approved after the committee, as had been expected, agreed to bar farmers and developers, known as "sodbusters," from receiving federal aid on any farmland if they have converted fragile, erosion-prone grasslands to cropping within the past five years.

Millions of acres of rangeland in the West, mainly in Montana and Colorado, has been plowed up and devoted to wheat production in the last decade, creating erosion problems that could take years to rectify, in the view of many soil experts.

The limitations on sodbusters had been expected to be included in the bill, but the committee then extended the benefits-payment ban to all highly erodible land that is cropped without a government-approved soil-conservation plan after 1988.

In another minor surprise, the committee agreed without discussion to include provisions in the bill that would require the USDA to carry out more research on organic farming methods. The proposal, sponsored by Sen. Patrick J. Leahy (D-Vt.), had been blocked in the committee for more than two years.

Despite warnings by Assistant Secretary Peter C. Myers that the USDA could get no more than 10 million acres of erosive land into the conservation reserve during the first year and that it faced a major task in persuading farmers to sign up, the committee insisted on a full-speed-ahead approach.

As envisioned by the legislators, the reserve would take tracts of land out of production for a minimum of 10 years and require that the soil be protected with grasses, trees and shrubs, which the government would provide to farmers on a cost-sharing basis.

Myers has estimated that the Agriculture Department payments will run about $40 per acre per year, or less than might have to be paid through other programs if the land were kept in federally subsidized grain production.