Sen. Jesse Helms (R-N.C.) yesterday continued his resistance to an alleged "ideological purge" of conservatives from foreign policy posts by blocking Senate action on more than 20 nominees for ambassadorships and senior State Department posts, aides to Helms said last night.

According to the aides, the "hold" put in effect by Helms covers the nominations of John Whitehead to be deputy secretary of state, Rozanne L. Ridgway to be assistant secretary for European affairs, Elliott Abrams to be assistant secretary for inter-American affairs, and such key ambassadorial nominations as Thomas R. Pickering to Israel, Richard R. Burt to West Germany and Winston Lord to China.

The aides said Helms had been joined by eight other Republican senators: James A. McClure (Idaho), Strom Thurmond (S.C.), Steve Symms (Idaho), Paula Hawkins (Fla.), Chic Hecht (Nev.), Orrin G. Hatch (Utah), Phil Gramm (Tex.) and Mitch McConnell (Ky.).

The aides said the nine senators sent a letter to Secretary of State George P. Shultz stating that, before they would allow a Senate vote on the nominations, they want to meet with him to discuss their concerns that conservatives are being replaced in too many posts by career diplomats and that some of Shultz's recommended nominees are people whose loyalty to President Reagan's policies is suspect.

Twenty-three conservative Republican senators took those complaints directly to Reagan last week. Symms said later that "the president shouldn't be surprised if some of the State Department appointments run into opposition."

Helms reportedly said at the meeting that he would hold up approval of John D. Negroponte, ambassador to Honduras, to replace James L. Malone as assistant secretary for scientific and environmental affairs unless Malone is given another assignment.

The "hold" involves a form of senatorial courtesy under which other members tacitly honor a senator's request for delay of a confirmation vote. The rules of the Senate Foreign Relations Committee prohibit putting a hold on any nominee until that person has been cleared by the committee for a vote by the Senate.

Because of delays in filling diplomatic posts, the committee has been hit with a sudden rush of nominations this month. Although a precise figure was not available last night, committee sources said the number of nominees who have been cleared by the panel or who are slated for hearings shortly is between 20 and 30.

Other congressional sources said last night that Senate Majority Leader Robert J. Dole (Kan.) and other ranking Republicans, faced with so many posts going unfilled, probably will not wait for long before pressuring Helms and the others to remove the holds. The aides to Helms said the nine senators tentatively hope to meet with Shultz early next week and expect to be in a better position then to announce their next move.