After widespread publicity about Gov. Marvis Mandel's previously secret involvement in the purchase of a 200-acre farm, three of his partners in the venture arranged to sell the farm under one corporate name and buy it back secretly under a different partnership, according to testimony at Mandel's corruption trial today.

James H. Graves, one of the two publicly identified partners in the second purchase of Ray's Point Farm on the Eastern Shore testified today that "it just happened" that W. Dale Hess, William A. Rodgers and Harry W. Rodgers III kept their partnership in the venture secret. Hess and the Rodgers brothers are codefendants in the trial along with Mandel, Irvin Kovens and Ernest M. Cory Jr.

Graves' testimony came on the second day of the government's presentation attempting to prove charges that Mandel and the five codefendants secretly defrauded the citizens of Maryland through a series of hidden deals.

He said he and Louis Tabor agreed to purchase Ray's Point after publicity led its owners to put the property up for sale. At that point, Mandel bowed out of the venture, Graves said, as did Pimlico race track co-owner Nathan Cohen and another partner. But Hess and the Rodgers brothers kept their interest through a silent partnership in G & T, the name of the Graves-Tabor venture, Graves said.

The prosecution hammered away today at the hidden nature of the involvement of Hess and the Rodgerses in the second Ray's Point venture and of Mandel in the first.

The government alleges that Mandel, through such hidden deals, received about $350,000 worth of gifts from his codefendants. In return, the government alleges, the governor assured that state legislation would bring profits to the codefendants' businesses.

Pimlico co-owner Cohen concluded his testimony today. One of the sc members of the first group to buy Ray's Point, he said Mandel was given a $45,000 interest in the property because Hess said he took care of the governor by cutting him into business deals.

Cohen also said he had given an $8,000 campaign contribution to Mandel in 1971 because he believed that by giving a smaller contribution of $2,000 the year before, his track suffered by being assigned a poor schedule of racing days by the state Racing Commission.

"It has been my expericne that small campaign contributions had resulted in inferior treatment," Cohen said when asked why he had felt the contributions to Mandel would help his race track even though racing dates are awarded by the Racing Commission, of which the governor is not a member.