Tension between the new Republican administration and the new Republican chairman of the Senate Foreign Relations Committee was not eased inauguration night when Sen. Charles H. Percy wandered into a Democratic fund-raising dinner in Georgetown.

Chariman Percy strolled into the elegant house of the committee's senior Democrat, Sen. Claiborne Pell, where Democratic politicians were plotting a 1982 Senate campaign war chest. That brought a shout from a senator that Percy "has seen the light and joined the Democrats." No, said Percy, he was only looking for "my boarders" (daughter Sharon and her Democratic husband, West Virginia's Gov. Jay Rockefeller, who were at the dinner).

Political banter followed during which Percy thanked liberal Democrats who backed him against a conservative Democratic challenger in 1978. One diner later reported to the Reagan inner circle that Percy had called himself more comfortable at Pell's house that night than with freshman right-wing Republican senators. Others present say they cannot recall that being said, but the incident furthered the impression at the White House that Chuck Percy constitutes one big problem.

Whether he said it out loud or not, Percy does feel more comfortable with Claiborne Pell than with the Reagan crowd. That has been made clear by Percy's attitude on arms talks with Moscow, the Iranian hostage release, strategy on the Haig confirmation and selection of a deputy secretary of state.

Ronald Reagan is not the first president with a Percy problem. During 14 years in the Senate, Percy has exasperated Lyndon Johnson, Richard Nixon and Jimmy Carter, but especially Nixon. The difference now is that for the first time, Percy can exercise real power. He talks about wielding the gavel as he did long ago as the boy-wonder chairman of Bell & Howell, but the foreign relations post seems more truly the substitute for his frustrated presidential ambitions. As such, since the Nov. 4 election, Percy has been playing surrogate chief diplomat.

While unwilling to publicly attack Percy, Reagan's foreign policy advisers were shaken by the senator's post-election visit to Moscow. The furor over who leaked the secret cables reporting on his Kremlin talks obscured serious issues.

To this day, Percy insists he was transmitting the wishes of the new administration, as conveyed to him by national security aide Richard Allen and by Reagan himself, when he gave the impression of desire for SALT II talks to commence at once. Reagan's advisers say the wrong idea was given; only Soviet appreciation of how Washington works prevented a dangerous misunderstanding.

During the transition, Percy also seemed to be playing an activist diplomatic role, seeking release of the hostages. When Iranian Prime Minister Rajai visited the United Nations, said Percy, "I went to New York immediately to find out what was happening." When Deputy Secretary of State Warren Christopher was negotiating in Algiers, Percy was on the transatlantic telephone to him daily.

What has worried the Reagan camp is that the Iranians, less sophisticated than the Russians, would mistake Percy's voice for Reagan's. Percy has been extravagant in his praise of the Carter administration's deal with Tehran and Christopher's feat, a judgment that differes considerably from the Reagan camp's.

When Percy's first task as chairman was presiding over Alexander Haig's confirmation hearings, nervous Regan agents immediately worked out an agreement whereby tactical leadership would devolve to Senate Majority Leader Howard Baker. But even before Baker's incapacitating illness, Percy was regularly digressing from the agreed scenario offering concessions to his friend, Sen. Pell. Percy's agreement to subpoena Watergate tapes may well have won three Democratic committee votes for Haig as he claims, but it also infuriated the Reagan team.

The most recent difficulty was Percy's objection to naming California Supreme Court Justice William P. Clark as deputy secretary of state on grounds he did not meet Chrsitopher's standard. When asked by a Reagan aide where the objections were coming from, Percy replied: "They're coming from me." He explained he was concerned by derogatory "comments" about Clark he had heard at a Washington dinner of Stanford University's Hoover Institution.

Percy insisted on a consultation with Clark, which turned out to be a long grilling of the justice. The senator seemed mollified (though still unwilling to make a flat commitment), and Clark's nomination was sent to Capitol Hill.

All this is built on a base of hostility. The president's insiders felt that Reagan's laying of arms around Percy in his 1978 reelection scare never was adequately appreciated, as reflected in the senator's $500 campaign contribution to John Anderson for president. When Reagan insiders call Percy a "loose cannon," that is one of their gentler descriptions not made public. Such biting of tongues about Percy at the White House may not last forever.