A House subcommittee was urged yesterday to support legislation requiring foreign investors to report purchases of U.S. farm land to the secretary of Agriculture.

A stronger bill, proposed by Rep. John B. Breckinridge (D-Ky.), would prohibit such investments altogether, but got little attention at the hearing before the Agriculture subcommittee on family farms.

There have been numerous recent reports that foreigners are buying up significant amounts of U.S. farm land, but there is little hard information available. The various bills dealt with yesterday are intended at the least to make such information centrally available.

Although Department of Agriculture statistics show less than 1 percent of U.S. farm land in foreign hands, congressmen sponsoring the bills insist that current monitoring of sales is inadequate to determine if restrictions are needed.

Subcommittee chairman Rep. Richard M. Nolan (D-Minn.) said substantial increases in foreign ownership would threaten family farm holdings and local tax bases and potentially influence American agricultural production.

Nolan pointed out that witnesses from the departments of Treasury, Commerce and State all acknowledged an absence of information on the extent of foreign buying.

"This legislation is not punitive, but it is (an attempt) to give us some of the information we are now so woefully lacking," said Rep John H. Krebs (D-Calif.).

Department of Agriculture spokesman Howard W. Hjort declared the proposed bills premature. The department has two surveys of foreign holdings under way.

Agriculture's 50,000-sample survey of farm lands, including ownership and use, will provide information this year, and a study of whether extensive farm land monitoring is feasible will be completed late in 1979, according to Hjort, director of economics and policy analysis.

To undertake a registration of sales to foreigners of the scope the proposed bills would require is too costly and time-consuming for the department, Hjort told the subcommittee.

"I have to wonder if you're really testifying for the Department of Agriculture or the Office of Management and Budget," Rep. Berkley W. Bedell (D-Iowa) replied.

National Farmers Union spokesman Reuben Johnson, implying that administration members have resisted the bills as interference in foreign policy, told the committee he believes "other agencies may be leaning rather heavily on Agriculture not to do anything."

Sen. Herman E. Talmadge (D-Ga.) last month released a General Accounting Office study showing only three tenths of 1 percent of farm land in five states surveyed was foreign-owned.

Talmadge has asked for more extensive surveys by GAO and sought a $450,000 appropriation to increase Agriculture Department's monitoring of foreign purchases.