The bulwarks and revetments around the Pentagon are pocked these days from the bursts of political mortar fire. Of itself, this would not be too unusual, especially in a presidential election year.
But what makes this barrage from the higher ground of Capitol Hill especially interesting - and embarrassing for the Reagan administration - is that it comes mainly from Republicans. Weapons testing, contract warranties, spare-parts prices, auditing procedures, the revolving door between the armed services and defense contractors: On a variety of important issues that get to the heart of how well the Defense Department is managed, members of President Reagan's own party are hammering away with critical volleys.
* Sen. Mark Andrews of North Dakota calls the Pentagon's objection to a new-weapons warranty law ''a smoke screen covering its refusal to go along . . . with the first systemic reform in the past 30 years.'' In congressional testimony the other day, Senator Andrews quoted former President Eisenhower's warning against ''the acquisition of unwarranted influence . . . by the military-industrial complex.''
* Rep. Jim Courter of New Jersey is pushing a ''creeping capitalism'' bill, which would force the Defense Department to seek more competitive bids for weapons contracts.
* Sen. Nancy L. Kassebaum of Kansas wants to know why the Pentagon has delayed setting up a new independent weapons testing office accountable to Congress.
* Sen. Charles H. Percy of Illinois last week criticized the large number of retired military personnel who go to work for defense industries. He cited several hundred former Air Force officials who joined a missile manufacturer, ''trading in their service stripes for pin stripes . . . cashing in with big salaries at the taxpayers' expense.''
* Sen. William V. Roth of New Jersey is highly critical of the Defense Contract Audit Agency, which he says ''should be scrutinizing defense contracts like an unforgiving Scrooge.''
Instead, he charges, it has become too intimate with the companies it is supposed to oversee, stifled the efforts of would-be whistle-blowers, and in large part ''left the taxpayers' defense dollar defenseless against excessive pricing and cost growth.''
This Republican sniping and the difficulty it causes the White House has several aspects. It is part of the traditional tension between the executive and legislative branches over responsibilities and ''turf'' which transcends party loyalties.
Part of it comes from the natural inclination of GOP lawmakers to be (or at least want to appear to be) businesslike and deficit-conscious. They find it frustrating when a Republican adminstration is seen to be at least indirectly responsible for newsmaking ''horror stories.'' Senator Percy's staff found it could get for free a three-inch piece of steel wire a contractor wanted to charge the Pentagon $7,500 for.
And part of it has to do with the difficulty of rooting out ''waste, fraud, and abuse'' - as the administration promised to do - in a massive bureaucracy of more than 3 million people (military and civilian) that disburses or consumes three-fourths of all federal procurement. Like the proverbial battleship, it takes a long time to turn it around - especially when the chief interest at the White House and among political appointees at the Pentagon is in pushing for the largest-ever peacetime military buildup.
The administration has had some success in improving defense management, even though it has had three deputy defense secretaries in three years and has had to let one go under charges of financial impropriety stemming from his pre-Pentagon days as a defense contractor. The No. 2 official at the Pentagon is in charge of day-to-day budget issues and management.
Most of the reports on spare-parts prices have come from within the Defense Department. Under Defense Secretary Caspar W. Weinberger, the Pentagon's inspector general (a post established in 1978) has become very active in rooting out questionable defense contracting practices. There is more competition in weapons buying (although as a portion of the total it remains relatively low). And such things as multiyear contracting have made for smoother procurement.
''In the main so far, they're moving in the right direction,'' the House defense appropriations subcommittee chairman, Joseph Addabbo (D) of New York, told reporters at breakfast the other day.
Still, there seems to be much reason for Republicans to criticize, especially regarding the Defense Contract Audit Agency (DCAA). The Defense Department has 9 ,400 auditors, 4,000 of whom work for the agency. Using company records, DCAA auditors assigned to defense contractors are supposed to make sure the federal government is being charged no more than is correct for goods and services.
But for years, the DCAA has had a problem with access to contractor records. Some companies resist auditing efforts, and critics say the agency is not tough enough in insisting that records be made available.
''Some of these access problems have existed for decades, not just years,'' Joseph H. Sherick, the Defense Department's inspector general, told the Senate Government Affairs Committee last week.
George Spanton, a recently retired DCAA auditor, told senators, ''My attempts to disclose waste and abuse of tax dollars by major defense contractors were met with hostility and rejection by my supervisors in the agency.''
''Not only was my work ignored,'' he said, ''but I was continually threatened with early and unwarranted transfer if I did not retire when my bosses wanted me to retire.''
The Merit Systems Protection Board (a federal agency) recently concluded that Mr. Spanton had been harassed and threatened, and recommended to an administrative law judge that Spanton's supervisors be disciplined.
The Air Force told another well-known whistle-blower, A. Ernest Fitzgerald, that he could not represent the Pentagon at the Senate hearings and disapproved his testimony, which was also critical of the DCAA.
Senator Percy (who may be facing a stiff reelection fight this year) termed this ''one of the most exasperating and frustrating situations I have ever faced.''