The Reagan administration is weighing whether to invoke a law authorizing the seizure of tax payments made by U.S. businesses operating in Panama, national security adviser Colin Powell said today. Saying that economic sanctions applied so far ``have not yet created enough pressure'' to force the ouster of strongman Gen. Manuel Antonio Noriega, Powell said ``we are examining additional pressure that might be brought to bear.'' He briefed reporters not long after giving the vacationing President Reagan an update on the Panamanian problem. A senior administration official, disussing Panama on grounds he not be publicly identified, said the United States would encourage any move within the Panamanian Defense Forces to oust Noriega. ``He still is firmly in control, but not as in control as he was, perhaps, a month ago, and every effort we can take to foster that discontent in the PDF, I can assure you we are taking,'' he said. ``If the PDF, after examining the situation, think it would be useful to remove General Noriega, I think that would be a very sound decision for them to take,'' the official said. Powell acknowledged that some corporations operating in Panama have balked at having their tax payments placed in an escrow account because of a concern that it could hamper their operations. For this reason, he said, White House advisers and other administration officials are studying the implications of invoking the International Emergency Economic Powers Act _ which would authorize the government to seize these payments. ``We have to be cautious before you invoke ... because it is a very powerful tool, and the staff back in Washington is examining the pros and cons'' of invoking the act, Powell said. ``And if it is a sensible thing to do, to continue to apply pressure on General Noriega, we will provide that for the president for his consideration.'' Powell refused to discuss any military options being weighed, except he indicated there would be no immediate dispatch of troops beyond the 1,300 deployed to the Central American country early this week. Powell, an Army lieutenant general, said he believes there now is ``a reasonable degree of security'' for Americans living in Panama and the U.S. installations there. Meanwhile, the administration was taking a dim view of Jesse Jackson's contacts with Noriega, despite Jackson's diplomatic coups in the past during visits to Cuba and Syria. Following Jackson's disclosure that he had sent a letter to Noriega two weeks ago asking him to resign, State Department spokeswoman Phyllis Oakley said Monday that such communications could prolong Noriega's grip on power. ``The proliferation of channels is a tactic Noriega uses to buy time,'' Ms. Oakley said. ``We have available channels of communication with Noriega if and when they are needed. We think it would be best to continue to use these channels exclusively.'' White House spokesman Marlin Fitzwater, traveling with Reagan in California, also criticized the Democratic presidential candidate's involvement in Panama. ``We have a bipartisan coordinated plan for dealing with Noriega,'' he said. ``That's why it's important to Congress and the public, and we believe it's been working.'' Jackson has dealt successfully in the past with other U.S. adversaries. In 1984, he traveled to Cuba and persuaded President Fidel Castro to release 26 political prisoners. He later went to Syria and, during talks with President Hafez Assad, won freedom for an American military pilot detained there. His efforts earned him an enthusiastic White House welcome. Jackson said he has no plans to travel to Panama to try to help resolve the 6-week-old crisis in that country. About 1,300 Army soldiers and Marines were headed to Panama today, joining the 10,000 troops stationed at the U.S. Southern Command in Panama. The Pentagon said the soldiers are being sent to increase security for Americans and U.S. facilities in Panama. In a related development, a former Panamanian official told the Senate Foreign Relations Committee on Monday that Noriega probably has evidence of complicity by U.S. officials in Central American drug trafficking. Jose I. Blandon produced a document Noriega sent to the country's U.S. diplomatic offices in February saying he has proof that American officials knowingly established policies that supported people in the drug business. Blandon, a former intelligence official and consul general who defected last year, mentioned Panama, Guatemala and Costa Rica. Jackson says he agrees with the Reagan administration that Noriega should step down, but he has accused U.S. officials of overkill in trying to achieve that goal through economic sanctions that have contributed to economic paralysis in Panama. Jackson, appearing Monday in Milwaukee, renewed his call for Noriega to leave Panama and released a letter in which Noriega rejected ``any political and economic program that will be dictated from Washington, D.C.'' ``My duration as commander and chief of the defense forces is governed by the Panamanian constitution and law of the defense forces,'' Noriega's letter said. While releasing the letter, Jackson renewed his call for Noriega to go into exile. ``I remain convinced that it is in the best interests of the Panamanian people for General Noriega to leave,'' Jackson said. ``Today I reiterate my public moral appeal for him to depart.''