WASHINGTON, Feb 20: Two high-ranking US senators on Thursday asked Treasury Secretary John Snow to look into whether big American companies are skirting US international sanctions by using offshore subsidiaries.

"It is important that US companies abide by the spirit as well as the letter of the law," said Sen. Charles Grassley, an Iowa Republican, and Sen. Max Baucus, a Montana Democrat, in a letter to Snow. Grassley is the chairman of the Senate Finance Committee, and Baucus is the panel's ranking Democrat.

The senators asked whether current laws and regulations are enough to keep companies from doing business with countries subject to sanctions enforced by Treasury's Office of Foreign Assets Control.

Independent foreign subsidiaries of American companies are allowed to trade with sanctioned countries, but Grassley and Baucus worry that the law allows a loophole for sham overseas subsidiaries that may be only post office boxes.

The senators also released letters to three companies - Halliburton Co., General Electric Co. and ConocoPhillips - asking about their subsidiaries' activities in Iran and Syria.

Halliburton, the Texas-based oil services giant, said earlier this month in a filing with the Securities and Exchange Commission that it had received a letter from OFAC seeking more information about its business dealings with Iran.

Representatives of all three firms said they had not broken any US laws. In response to Thursday's letter from the senators, a Halliburton spokeswoman said in an e-mailed statement: "Halliburton's business in Iran is clearly permissible under applicable laws and regulations. The activities of Halliburton's subsidiaries in Iran are staffed and managed by non-US personnel."

GE spokesman Gary Sheffer said his company's sales to Iran were done through independent subsidiaries that had been established decades ago. "If Congress decides to change those (law) provisions, GE will of course comply," he said from GE's headquarters in Fairfield, Connecticut.

A spokesman for ConocoPhillips issued a written response saying the company had a partial interest in a small natural gas plant in Syria, which will end in 2005.

"This investment started in 1999, in compliance with US laws and with full knowledge of the US government. This investment has been and continues to be permitted under US laws whether made directly by Conoco Phillips or through a subsidiary," the statement said. -Reuters