The new federal soil conservation reserve, designed to take erodible crop land out of production, has fallen short of first-year enrollment goals set by Congress, in part apparently because of competition from more lucrative farm-support programs.

Two sign-up periods this year have brought 3.8 million acres of fragile land into the reserve, about 75 percent of the 5 million acre goal in a program that is supposed to retire at least 40 million acres by 1990.

Conservationists contend that the shortfall is due partially to inadequate promotional efforts by the Agriculture Department and to budget limitations. USDA officials, expressing satisfaction with the sign-up so far, say that other programs that subsidize crop production have adversely affected the reserve.

"The biggest competition for the reserve is our own deficiency payment crop subsidy program," said Orin Hanson, of the Agricultural Stabilization and Conservation Service, which is overseeing reserve sign-up.

Hanson said "hundreds" of farmers have written to USDA saying that they found it more profitable to continue cultivating their most erodible land, for which they can get cash subsidies on major commodities, than to enroll it in the reserve.

Deputy Secretary of Agriculture Peter C. Myers, formerly Soil Conservation Service chief, agreed. "We're fighting -- or bidding against -- our own farm programs . . . . The deficiency payments, even on marginal corn land in places like Missouri, are higher than what we can pay in the reserve," he said.

The reserve was established by Congress last year to pay farmers to convert fragile land to soil-holding grass and trees and keep it out of production for at least 10 years. USDA is paying an average annual fee of about $44 per acre, although some payments run as high as $90 per acre in the fertile Corn Belt.

Hanson noted that farmers in the high-yield areas can get subsidy payments that range $35 or more per acre above what they would receive from the conservation reserve. But in other cases, he said, such as the cotton area of west Texas, farmers enrolled heavily during the second sign-up period after they realized the conservation benefits would be higher than crop subsidies.

But Robert Gray of the American Farmland Trust, one of the organizations that lobbied for the reserve last year, argued that enrollment would have been heavier had USDA and the Office of Management and Budget slightly raised the bid acceptance levels. Reserve entries were accepted on the basis of bids made by farmers.

"OMB is really cheap. For another dollar per acre they could have enrolled another 1 million acres. That is cheap," Gray said. "They just haven't analyzed what could be saved in spending on the other subsidy programs by raising the bid acceptance levels. They could go to an average of $50 per acre on reserve land and still save money in the long run."

Daniel Weiss, Sierra Club lobbyist, added, "The average bid is around $44. Last year, during the farm bill debate, they were predicting averages of $55 to $60. They are going to have to offer more money to attract more folks into the program. There is a lot of erosive land in Illinois and Iowa that should go out of production, but it won't at the rates that are being offered."

Myers, however, said OMB had accepted the department's recommendations on bid levels without argument during both sign-up periods. "There still will be a net cost to the government for the reserve program, no matter what anyone says," Myers said. "OMB acted very quickly, and we were pleased."

Myers and Hanson said another important factor influenced the determination of bid levels. "We don't want the reserve to be competing with cash rent prices for farm land. We don't want to make the program so attractive that landowners will put all their rental land in the reserve. We have to be careful not to put tenant farmers out of business."

Hanson said that, for this reason, USDA tailored bid acceptance levels in different parts of the country not to exceed customary cash rental rates. "We have had a concern for those farmers who must rent land. Our bid levels are close to what cash rents are."

Short of its first-year goal by about one-fourth, the reserve program now faces another major test. The second-year target set by Congress is 10 million acres, and Weiss and Gray say they think that higher payment rates and better USDA promotional efforts will be required to come close to the goal.

"The program is now six months old, and people understand it better," Weiss said. "But the department has a long way to go -- so far, only 6 or 7 percent of the 69 million acres that are eroding the worst have come into the program. They should be reminding farmers that after 1990 they can get no federal farm program subsidies if they do not meet soil conservation requirements. Every USDA office ought to have a huge poster advertising this."

Myers said word of this tough new requirement will filter out soon enough. "As the agricultural community realizes the compliance requirement is there, they'll be putting that erodible land into grasses," he said. "I don't think farmers are quite yet aware that they won't get these federal benefits if they don't have an approved conservation plan."