Prime Minister Margaret Thatcher told the House of Commons on Thursday that she welcomed New York City Mayor Ed Koch's change of heart on the subject of Northern Ireland. Koch completed a six-day tour of Northern Ireland and returned to New York, where on Wednesday he publicly disavowed his earlier opinions about the British stance on the troubled province. Koch said he accepted the British army as a peacekeeping force rather than an occupying army. Mrs. Thatcher told members of Parliament in the elected lower chamber: ``If more people came with an open mind and looked at what is happening on the ground, we would have many others making similar remarks.'' ``I admire Mr. Koch's forthrightness and I am glad he took time to come to Northern Ireland,'' she added. In Belfast, Koch was described as one of the few American politicians of stature who have had anything positive to say about Britain's role in Northern Ireland. ``His comments after his factfinding visit to Ireland are as refreshing as they are surprising'' the Belfast Telegraph, Northern Ireland's independent evening newspaper, commented editorially on Thursday. ``Compare his statement `My impression is that the British are trying to play a constructive role' with the attack launched by Congressman Joe Kennedy after his visit earlier this year'' the newspaper said, refering to the Democratic U.S. representative from Massachusetts. ``Mr. Koch has shown an attitude uncommon in American politicians when dealing with the Irish problem _ a willingness to view the situation with an open mind. ``He is also honest enough to admit that his vision of Ulster from across the Atlantic did not square up with what he found here: `I do not believe that they (the British) deserve the castigation that many of us, myself included, have heaped upon them,''' the Belfast Telegraph quoted Koch as saying. ``Too many people in the international community mistake the myths and propaganda emanating from these shores for facts and believe a British withdrawal is the simplistic solution to all our ills. Mayor Koch realizes the problems are much more complex than other `green-tinted' visionaries understand,'' the newspaper said. ``Of course, the hardline Irish-American lobbyists will attempt to make political capital from his comments but those Americans who are willing to listen will learn much more about the reality of life in Ireland today from Mayor Koch. ``They should, as must the people of Ulster, learn that harboring grievances for past errors or wrongs will not further the quest for peace here,'' the newspaper said. ``There have been historical mistakes in Ireland, on all sides, but acknowledgment should also be given, as Mayor Koch does, for the positive contributions made in areas like housing, jobs and electoral representation. We can build on gains not divisions.''