With its chairman pledging to take a "pretty tough attitude," a presidential commission launched its investigation of Pentagon procurement practices yesterday with a briefing from Defense Secretary Caspar W. Weinberger.

Commission Chairman David Packard told reporters that Weinberger deserves credit for trying to improve the system of buying and maintaining weapons.

"But, as I've said before, I intend to take a pretty tough attitude," Packard said after meeting with Weinberger. "We're not going to accept all the answers we hear. We're going to try and find some positive action we can recommend."

The 15-member panel, set up in the wake of defense contractor scandals, held a three-hour organizational meeting yesterday. Weinberger outlined his efforts to reform procurement polices, according to informed sources.

Weinberger initially argued against an independent commission investigation, believing it reflected badly on his stewardship, Pentagon sources said. But he eventually approved the idea after he was given veto power for the selection of panel members, according to a source.

Rhett B. Dawson, a former staff director of the Senate Armed Services Committee, will serve as the panel's staff director and Herbert E. Hetu, a former director of public affairs for theCIA, as counselor for public affairs.