Defense Secretary Frank C. Carlucci says he hopes to curb Pentagon purchasing abuses by ordering new limits on the number of ``final offers'' that defense contractors can make on a single deal. Carlucci said at a news conference Monday that he was surprised to learn how frequently companies were allowed to revise supposedly final bids, although he described it as ``the exception'' rather than the rule. In the past, contractors have been allowed to amend their final offers in consultation with the Pentagon to change prices or technical specifications to meet military needs. The Pentagon has been rocked in recent weeks by allegations that private consultants working for defense contractors bribed top military purchasing officials for secret contract information. Many of the alleged abuses disclosed in the Justice Department investigation involve contractors who, through the consultants, learned the price or other specifics of bids by competing companies, and then submitted a new ``best and final offer'' tailored to win contracts, some of them worth billions of dollars. ``It is the `best and final offer' that seems to us to create the most intensive point in the competitive cycle. And that means that information is at a premium,'' Carlucci said. ``We intend to continue with our competitive process. But when you repeat it once, twice, or three times, then it can readily become subject to abuse,'' Carlucci added. Carlucci, who was scheduled to testify before the House Armed Services Committee today, also said his aides had drawn up a ``protocol'' for the military to follow as more information is disclosed from the Justice Department investigation. Carlucci said the department has: _Required that 17 companies implicated in the investigation certify they did not engage in ``illegal or improper activity'' to obtain a defense contract; _Required those 17 to agree, in any new contract greater than $100,000, to include a clause allowing the government to recover profits or 10 percent of the contract value if the deal is tainted; _Started procedures to lift the security clearances of six people, including one suspended without pay from the Navy Department and five others transferred to other duties pending results of the investigation; _Sent letters to the top 200 defense contractors urging them to implement strong internal ethics programs, ``stringent management controls, and asking them to report back to us on their self-governance programs;'' _Reviewed federal acquisition regulations to tighten controls on consultants employed by defense contractors; _Formed an audit task force to review the cost imposed on the military budget by consultants employed by private defense contractors. Carlucci said the certification requirement was being applied only to the 17 implicated companies to avoid penalizing contractors who were not under suspicion. ``This is a rifle action. It is not a shotgun action,'' he said. ``We are directing this at certain contractors. We do not intend to apply it indiscriminately, because it does impose a burden on people. ``And where there are burdens, there are costs, and those costs may come back to the Pentagon and the U.S. taxpayer,'' he said. ``It is only where we have reason to believe that people are under suspicion that we are doing this.'' Carlucci declined to identify people whose security clearances were being lifted, saying only that ``we are taking steps to revoke the security clearances of individuals who have been involved in illegal or improper actions.'' In a related development, the White House announced that President Reagan intends to nominate Milton L. Lohr to the new position of deputy undersecretary of defense for acquisition. Since 1983, Lohr has been president of the Defense Research Corp. in La Jolla, Calif. Before that, he was executive vice president of Flight Systems Inc., from 1969-83. Lohr, a 63-year-old native of Revere, Mass., graduated from the University of Southern California in 1949 and the University of California at Los Angeles in 1964.