Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.) says more time is needed to seek a compromise on the politically sensitive extradition treaty between the United States and Britain, but "real progress" is being made.

On Tuesday, Lugar had offered to amend the treaty to meet objections that have kept it stalled in the committee since last fall. But on Friday, he postponed a committee meeting on a new version of the pact to allow more time for talks on a compromise.

He said he thinks that a compromise acceptable to a majority of the Senate and to the British government will be ready sometime this week.

The treaty has become a source of considerable irritation in U.S.-British relations because of its relationship to efforts to combat international terrorism.

At issue is Britain's desire to get a new treaty that will make it easier to extradite Irish Republican Army members charged with crimes in Britain.

Prime Minister Margaret Thatcher has been urging approval of a new treaty, signed by the two governments a year ago, as an indication of American seriousness about fighting terrorism. She stepped up her efforts after allowing U.S. warplanes to take off from British bases to bomb Libya on April 15.

In a radio address last Saturday, President Reagan said failure to ratify the treaty would be "an affront" to Thatcher and would give terrorists "a safe haven" in the United States.

The new treaty was negotiated with the aim of ending an exemption that has allowed four IRA fugitives to escape extradition by claiming that the offenses with which they were charged in Britain were politically motivated acts. But many members of Congress, concerned about the reaction of American opponents of British rule in Northern Ireland, have been reluctant to vote for ending the political exemption.

To ease these concerns, Lugar is proposing several changes. They include eliminating "possession of firearms" from the list of offenses that no longer would be considered political, making provision for special review by the federal courts of each extradition request and permitting the president to deny extradition in cases where he makes a finding of "humanitarian" considerations.