A 79-year-old British historian, who went to work at the US Library of Congress on the life of former secretary of state Henry Kissinger, was herded on arrival in a wheelchair at Washington's Dulles airport to a small room facing a superintendent with a revolver in his hip for no apparent mistake.

Although all his travel papers were in order, ``I was stopped and treated rather disgracefully,'' lamented Sir Alistair Horne at a conference in Washington Tuesday.

Stringent enforcement of US visa policy and overzealous immigration officers following 9/11 are not only scaring off foreign students and tourists but dampening the investment climate and taking a toll on the economy, experts told the conference organized by the Center for Strategic and International Studies in Washington.

Among the other cases cited to highlight the economic, security, scientific and diplomatic implications of changes in US visa policy were:

An international business conference in Hawaii had to be shifted to Hong Kong because the organizers could not obtain travel papers for most of its participants, who were from China.

Some of US aviation giant Lockheed Martin's testing of its civil space activities have been delayed because visas could not be obtained on time for Russian scientists.

A company in northern Illinois waited in vain for seven months for its prospective buyers from China to get a visa to inspect its products and close a multi-million-dollar sale. Eventually the company became bankrupt and was auctioned off.

American businesses lost nearly US$31 billion (HK$241.8 billion) in sales between 2002 and 2004 because foreign executives could not get into the country to purchase US goods and services or attend trade shows, a private-sector study showed.

From 2003 to 2004, there was a roughly 30 percent decline in the number of applicants for US graduate programs and correspondingly 20 percent decline in admissions, university figures showed.

The situation is critical and requires the personal intervention of President George W Bush, former defense secretary Frank Carlucci told the conference. Bush should act to stop further erosion of US popularity overseas, he said.

``It is part and parcel of the anti-Americanism around the world, and if the president is serious about addressing that, in that context, he has to address visa policy.''

``President Bush can demonstrate leadership and demonstrate that the country is not anti-foreigner and that we are not closing the gates, and he can encourage the bureaucracy to make sense out of a patchwork quilt. It is slowly coming together but needs to come together much faster.''

Lockheed Martin international business development executive Richard Kirkland said ``what is important is predictability and process'' of getting approval for visas.

Nearly 100 percent of aerospace programs in the US involve some form of foreign participation or content, he said.

America's post-9/11 visa policy threatens economic security, said Don Manzalo, head of the small business committee at the House of Representatives. ``Reforms are needed to boost US exports, maintain our technological leadership and create jobs.'' Multinationals ``are setting up shop overseas to avoid our arbitrary visa process,'' said Monzalo, who is campaigning for a fast-track visa program for companies.

He had brokered a deal between the US and China earlier this year, allowing executives to travel between the two countries under a single visa for 12 months instead of seeking new visas for each trip.

The Migration Policy Institute, an independent think-tank that studies movement of people worldwide, said it was convening a bipartisan panel of US lawmakers, business leaders and public policy and immigration experts to consider immigration reforms.

``Neither national security nor individual liberties can be properly safeguarded in the United States without sensible and effective immigration laws,'' said Lee Hamilton, who was among on a special commission that investigated the 2001 attacks.

William Webster, former CIA and FBI head, said by scaring away foreign students, ``we are losing an opportunity for public diplomacy because the best ambassadors we can possibly have are these students.''

Jordan's ambassador to Washington Karim Tawfiq Kawar said there has been a drop of more than 30 percent of students from the Arab world coming to the United States to study.