Robert A. Rowland, head of the Occupational Safety and Health Administration (OSHA), owns up to $50,000 in stock in a conglomerate that could be affected directly by Rowland's decision not to adopt a federal standard requiring clean drinking water and toilet facilities for farm workers.

Rowland owns between $15,000 and $50,000 in Tenneco Inc., whose Tenneco West agribusiness subsidiary owns more than 1 million acres of farm land and employs several thousand field hands in California and Arizona, according to his financial disclosure forms and company records.

His Tenneco stock is among Rowland's more than $1 million in holdings in chemical, pharmaceutical, petroleum and other stocks in firms potentially affected by recent OSHA decisions.

Rowland's role in decisions affecting those companies has prompted the federal Office of Government Ethics to begin a review this week at the request of Rep. Augustus F. Hawkins (D-Calif.), chairman of the House Education and Labor Committee.

Rowland was not available for comment yesterday, but OSHA spokesman Jack McDavitt said Rowland saw no potential conflict of interest because his decision will have "little or no impact" on the value of Tenneco stock. "I am sure that the field sanitation standard would not affect any stock more than a penny," McDavitt said.

A spokesman for the Migrant Legal Action Program (MLAP) said yesterday that adoption of a sanitation standard could have required Tenneco West to install, at considerable expense, more toilet facilities in California and more toilets and drinking facilities in Arizona.

"He is the fox guarding the chicken coop . . . . He should have recused himself from decisions affecting Tenneco," MLAP attorney Charles Horwitz said.

Several years ago, complaints of unsanitary Tenneco facilities were filed in California by 25 members of the United Farm Workers Union. The workers were fired and then reinstated after a second complaint to California officials, Horwitz said. Company officials were not available for comment.

Rowland, a former Texas lawyer and top Republican campaign official, has participated in several OSHA decisions affecting companies whose stock he owns. He does so under the terms of a "limited waiver" granted to him last September by then-Labor Secretary Raymond J. Donovan.

That waiver allowed Rowland to participate in broad policy decisions and rule making, such as enacting new standards, but it did not apply to specific OSHA decisions pertaining to individual companies.

Sources said yesterday that Donovan's waiver was not approved by the Office of Government Ethics and that it would be reviewed as part of the examination of Rowland's activities.

MLAP, which represented farm workers in the 13-year effort to enact a sanitation standard, said it believed the waiver was "too broad" and that such waivers were intended to apply only in cases of "insignificant interest . . . and we don't think $50,000 is insignificant."

Rowland's stock is held in a "qualified blind trust" approved last year by the ethics office. Under rules of the trust, Rowland is informed of any sales of his stock, and as of April 10, no stock had been sold, Rowland has said.

Rowland was a recess appointee by President Reagan last year, and has not been confirmed by the Senate. Labor Department sources have said that Labor Secretary William E. Brock is considering a replacement for Rowland, who has been strongly criticized by organized labor.

The ethics office is reviewing Rowland's role in OSHA's handling of proposed standards to regulate formaldehyde, benzene and ethylene oxide. Rowland has participated in decisions on those substances while holding stock in Exxon, Eastman Kodak, Monsanto, Tenneco, and other firms that have opposed the proposed regulations. CAPTION: Picture, Rowland has over $15,000 in Tenneco shares.