President Reagan's continuing problem with the Republican chairman of the Senate Foreign Relations Committee surfaced again when Sen. Charles H. Percy of Illinois compared notes with another committee member.

He was Sen. Paul Tsongas, a liberal Democrat from Massachusetts. The subject was Dr. Ernest Lefever, whose confirmation hearings as assistant secretary for state for human rights were just beginning. Percy was boyishly eager to find out whether Lefever had said the same outrageous things to both senators.

He had. Lefever, an ordained minister unlearned in the ways of Capitol Hill, made the tactical error of telling both senators that "the communists" opposed his nomination (based on Izvestia's attack). That was enough for Percy. From then on, the chairman made no effort to shepherd his president's nominee through the Senate.

A personal telephone call from Reagan a few days later did not move Percy.

On this, as on other issues during his five months as chairman, Percy has shown greater sensitivity to the desires of his committee's Democrats than to the president. That has unwittingly allied him with efforts by the Democratic left to undermine Reagan.

Tsongas, a 40-year-old first-term senator, in his understated way, helps lead that effort. While preaching a "new" liberalism, his votes never waver from the "old" liberalism of his Massachusetts colleague, Sen. Edward M. Kennedy. While professing that "as a rule, I would want to give the president his nominee," he opposed four earlier Reagan nominees (including two Cabinet members) on the floor and one other in committee.

There has been an undisguised pattern of Senate confirmation trouble for any nominee embracing the frequently radical ideology Ronald Reagan long has preached. Lefever echoes Reagan's view that friendly authoritarian governments should receive softer treatment than unfriendly totalitarian states.

Tsongas candidly says he would vote against Lefever even if there were no conflict-of-interest allegations that some critics privately admit were an afterthought. Nor is the problem with Lefever his often heavy-handed manner. aThe problem is ideology.

"That's why we're sticking with him all the way -- because its ideological," one senior Reagan aide told us. Presidential counsel Edwin Meese III is particularly adamant on that point, whenever told that Lefever is a hopeless congressional witness and probably an unfortunate appointment.

Ideology explains the half-dozen or more Reagan appointees whose withdrawals have been demanded in the Senate, beginning with Al Haig as secretary of state. Reagan and his senior aides agree that once the yellow feathers were shown on one appointment, there would be no end to Senate censoringl of his administration.

None of this has made much impact on Chuck Percy. He has maddened the White House from the beginning by bending to Democratic demands in the Haig confirmation, asking that William P. Clark withdraw as deputy secretary of state and not restraining the Democratic inquisition of conservative Tom Pauken as head of ACTION (the Peace Corps parent agency) because he was an Army intelligence officer in Vietnam. c

Nobody accuses Percy of trying to sabotage the Reagan administration. Rather, his Senate Republican colleagues think he finds it difficult to oppose either liberal Democrats on the committee or liberal opinion generally. While not sharing Tsongas's rigidly uniform application of human rights standards to friends and foes alike, he and Tsongas share a common revulsion toward any "kook" who thinks the communists are after him.

There is little tolerance for this in the Senate Republican cloakroom. Sen. Orrin Hatch of Utah, who helped save Percy from imminent defeat in 1978 by urging conservatives to vote for him, is furious. Sen. Jesse Helms of North Carolina, the committee's second-ranking Republican, revels in hopes that Percy might get rolled by the Senate on Lefever.

At the White House, there is belief Lefever would be in little trouble today were it not for chairman Percy. That brings no public cries of outrage but, instead, undeniably show handling of Percy's judgeship selections. If Percy really wants his choices on the federal bench, say the president's men, he ought to ask his good friend Paul Tsongas for help.