The Department of Agriculture has abandoned a policy that would have placed a secrecy label on thousands of public comments on the administration's proposed soil conservation plans.

The policy had been laid down by John B. Crowell Jr., an assistant secretary, on the ground that reporters and others, if allowed to view the comments, would emphasize the negative.

Except in cases involving trade secrets, public comments on proposed federal regulations and other actions by USDA are routinely available for public viewing before USDA makes its decisions on proposed regulations and other actions.

But Crowell, according to departmental officials, feared that negative comments would be "blown out of proportion" and put Secretary John R. Block under undue pressure to alter his much-criticized proposals for protecting farmland from excessive erosion.

Here and in its state offices, USDA is tabulating more than 60,000 comments on the proposals, which stress targeting of federal assistance on the most erosive land, a politically sensitive step that could entail moving many Soil Conservation Service technicians to new assignments.

Crowell's secrecy policy was dropped last week after Des Moines Register reporter James V. Risser, who had been denied a look at the comments, filed a Freedom of Information Act request for access.

Crowell's chief aide, deputy assistant secretary Richard D. Siegel, said the department decided its no-disclosure rule could not be sustained and it was dropped.

The comment period on Block's soil-protection plan closed at the end of January. A review team is expected to take at least a month to tabulate the thousands of written comments, which the department may use to alter its original proposals. A summary of the comments will be published in the spring.

The department is under a congressional directive to prepare an inventory of erosion problems nationally and develop a long-term program for dealing with them.

Block has called wind and water erosion critical, with topsoil loss that USDA calls "intolerable" occurring on some 143 million acres, more than a third of U.S. cropland. But the Reagan administration's fiscal 1983 budget proposes a substantial reduction in spending by the Soil Conservation Service and a sharp cut in some cost-sharing programs.

As part of the secretary's long-term plan, $10 million would be turned over to the states on a matching-grant basis in fiscal 1983 to attack local erosion problems. Federal spending and technical aid also would be concentrated in the most erosive areas.

The new targeting approach, although authorized in the 1981 farm bill, has caused widespread controversy. Farmers and legislators from areas where erosion problems are less severe have complained that Block's plan will cut them out of money and assistance they have received under existing programs.

The secretary is expected to publish his final program proposal in late spring.