Seven Democratic congressmen said yesterday they have written the White House attacking the appointment to the Commodity Futures Trading Commission of David Gartner, who has admitted he was given stock worth $72,000 by a prominent grain dealer.

Four of the House members called on President Carter to demand Gartner's resignation and the other three said Gartner at least should be named chairman of the commission.

All seven critics are members of the House Agriculture Subcommittee on Conservation and Credit, which oversees the CFTC, but has no authority over appointments, a duty vested in the Senate.

The President defended Gartner's appointment during his news conference Wednesday's saying he did not believe Gartner was in a conflict of interest. A White House spokesman said yesterday there has been no additional response to the two groups of House Democrats.

Gartner himself made public the gift to his children of $72,000 worth of stock in Archer-Daniels-Midland Co., a Minneapolis grain firm. The stock came from ADM Chairman Dwayne Andreas and his daughter Sandra McMurtie, who once was Gartner's secretary.

Gartner revealed the gift during a one-day Senate review of his nomination last month, and said he would disqualify himself from any CFTC decisions affecting ADM.

Gartner for many years was the top aide to Sen. Hubert Humphrey, and House members suggested privately his appointment was rushed through the Senate because the job was "a death wish" of the late senator and vice president.

In the letter calling for Gartner's resignation, the House members told Cater, "Although Mr. Gartner has pledged to disassociate himself from any CFTC decisions which could directly affect his friend's business, we are concerned that the existence of this fund could call into question in the minds of many people the credibility of the commission."

"Almost any decision concerning the commodities market could impact on ADM's wide-ranging operation," they pointed out. The Minneapolis flour and cattle feed company is a major dealer in soybeans, wheat and corn and is a big grain exporter.

The call for Gartner's resignation was sounded by Ed Jones of Tennessee, chairman of the committee subcommittee that oversees CFTC, and Floyd Fithian of Indiana, Berkley Bedell of Iowa and Fred Richmond of New York.

Three other Democrats on the subcommittee - Tom Harkin of Iowa, Dan Glickman of Kansas and Leon Panetta of California - declined to sign Jones' letter, instead sending their own, milder, protest.

Asserting that "serious questions . . . have been raised about Mr. Gartner's ability to serve on the commission without a conflict of interest," they said he should not be given the commission chairmanship.

That job is expected to be open up this fall, when the term of William T. Bagley expires. Gartner was named to replace John T. Rainbolt, who had been the commission's vice chairman until he resigned. The three congressmen urged Gartner also be denied that office.

At a press conference, Fithian said, "I don't know of a member of Congress who would not dismiss a staff member who accepted gifts of this magnitude" and said Gartner has "no compensating qualifications" for the job.

Other than his close friendship with one of the country's biggest grain dealers, Gartner has no familiarity with the work of CFTC, the critics complained.

Archer Daniels-Midland Chairman Andreas was the biggest single contributer to Humphrey's presidential bid in 1968. In 1974 he was acquitted of a charge of making an illegal corporate contribution to Humphrey's campaign.

Despite his long, close ties to Humphrey, Andreas contributed $25,000 to Richard Nixon's campaign in 1972, and the money eventually was used to help finance the Watergate burglers.