Rep. Daniel J. Flood (D-Pa.) announced yesterday that he will not run for reelection as chairman of the Labor-HEW subcommittee of the House Appropriations Committee.

Flood is currently on trial on charges that he took bribes in exchange for his help in obtaining federal grants.

In a letter to House Appropriations Committee Chairman Jamie L. Whitten (D-Miss.), Flood requested "that my name not be considered for election to chairman of the Appropriations subcommittee for Labor-HEW." At the same time, he made clear that he intends to continue "serving on the Appropriations subcommittees of Labor-HEW and Defense."

Rep. William H. Natcher (D-Ky.), chairman of the District of Columbia subcommittee of Appropriations, is expected to be Flood's successor as chairman of the Labor-HEW subcommittee.

Natcher is fiscally conservative, while Flood is liberal, a fact that could change the tenor of the subcommittee that funds major social programs of the two departments in its jurisdiction.

Natcher could be expected to do a more vigorous job of oversight on those programs. But whether his chairmanship would change the funding levels is unclear, since Natcher is one of only three conservatives on the 11-member subcommittee.

Appropriations subcommittee chairmen are nominated by the Democrats on the full Appropriations Committee, but must be elected by the caucus of all House Democrats and approved by the House.

House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) said yesterday that he believed Flood "would have had grave difficulties" being reelected subcommittee chairman.

O'Neill denied that he put any pressure on Flood not to seek the chairmanship. "It was Flood's decision. He made it," O'Neill said.

Natcher's relinquishing of the chairmanship of the D.C. subcommittee could leave that committee with the prospect of a freshman as chairman, since all other veteran members of the subcommittee chair other Appropriations subcommittees, except Rep. Charles Wilson (D-Tex.)9 An aide to Wilson said he did not want the chairmanship. The other members can chair only one subcommittee.

This year marks a major turnover in the chairmen of the Appropriations subcommittees, with five of the 13 getting new chairmen.

A liberal, Joseph P. Addabbo (D-N.Y.), will replace retired conservative George H. Mahon (D-Tex.) as chairman of the defense subcommittee. That change could make a major difference, since three other conservative members of the subcommittee also retired, and the level of defense spending could depend on who is chosen to replace them.

Rep. Robert B. Duncan (D-Ore.) is expected to replace defeated Rep. John J. McFall (D-Calif.), a member reprimanded by the House in the Korean influence-buying scandals, as chairman of the transportation subcommittee. And Rep. Adam Benjamin Jr. (D-Ind.) is expected to replace retired Rep. George Shipley (D-Ill.) as chairman of the legislative subcommittee.

Flood's announcement followed by a few days the announcement by convicted Rep. Charles C. Diggs Jr. (D-Mich.) that he would not seek reelection as chairman of the Africa subcommittee on the House International Relations Committee. Diggs was sentenced to three years for taking salary kickbacks from his staff, and is appealing his conviction.