A House subcommittee announced plans yesterday to hold hearings on reports that Sen. Jesse Helms (R-N.C.) tried to use his clout with the Reagan administration to influence a traditionally non-political U.S. Customs Service decision on tobacco tariffs.

In a series of letters last year, Helms urged Treasury Secretary Donald T. Regan to intervene personally in the case, saying a favorable outcome would be vital to his reelection to the Senate next year.

"Decisions regarding classification of imported goods have always been and must continue to be made on the merits of the particular case and without regard to any political considerations," said Chairman Sam M. Gibbons (D-Fla.) of the House Ways and Means Committee's trade subcommittee in announcing the hearings, which will be held in June.

"The subcommittee wants to examine allegations regarding improper political influence in this case," Gibbons continued.

Hill sources said that Gibbons felt the possibility that customs classification procedures had become politicized outweighed the traditional clubiness of Capitol Hill that would keep a House subcommittee from investigating a senator's actions. He and other members of the subcommittee fear that political interference in the customs procedures could undercut administration efforts to open new markets for American exports.

But Gibbons and two Republicans on the Trade subcommittee, Barber B. Conable Jr. (N.Y.) and Bill Frenzel (Minn.), wrote Regan two weeks ago expressing their concern that the Treasury secretary had given Helms "an advance commitment" that the tariff would be raised on the filler tobacco.

Regan replied that he had given Helms no commitment of a favorable ruling and enclosed a memo from Assistant Secretary John M. Walker Jr. directing Deputy Costoms Commission Al DeAngelus "to make this classification decision as you would in any other case, solely on the merits and without regard to any political consideration."

A Treasury spokesman said the Customs Service sent its decision to Walker last week. But Walker returned it after noting that all Customs officials involved in the case had not signed off on it.

In the letters, Helms asked Regan's support for a petition by a North Carolina tobacco farmer that would double the tariff on imported tobacco used a filler by American cigarette makers. Similar petitions had been denied twice before.

After publication of the letters, obtained under the Freedom of Information Act, Helms denied wrongdoing and said he had never asked Regan "to make an improper decision.