Defense contractors and Pentagon procurement officials are under harsh criticism that could rebound politically against the Reagan administration. * A congressional investigation alleges that the nation's largest submarine builder knowingly submitted low bids that resulted in multimillion-dollar cost overruns to which US Navy officials acquiesced.
* Another legislative panel finds that major defense suppliers routinely charge the government for questionable public-relations costs because Defense Department regulations are lax.
* The Navy's topline fighter, the F-14A Tomcat, is said by Navy Secretary John Lehman himself to have serious engine problems that have resulted in 24 crashes. Navy officials also have refused to accept a batch of very expensive air-to-air missiles because of doubts about quality.
* The US Army, after many years and 61 accidents that cost 223 lives, has grounded 500 helicopters for safety modifications.
Officials defend the administration record by asserting that many of these problems were inherited. And they point out that in many instances, the Pentagon and military services themselves brought them to light. Officials also say that the administration has taken many steps to correct such abuses. Still, the administration is very sensitive to charges that it has not rooted out ''waste, fraud, and abuse'' in defense spending as Ronald Reagan promised, in his 1980 campaign, to do.
Defense Secretary Caspar W. Weinberger, in a press conference this week, bristled at suggestions that corruption or inefficiency in defense contracting have anything to do with military readiness. ''There isn't any to start with, and it has had no effect,'' he said.
In a speech a few days earlier, Weinberger cited 657 convictions - ''almost twice as many as last year'' - of contractors who had tried to defraud the Pentagon.
Democrats, however, accentuate the negative in their criticisms of the Reagan administration record on weapons procurment and defense management.
''You did not vote to pay 50 bucks for a 50-cent light bulb,'' Walter Mondale said in his speech accepting the Democratic presidential nomination, referring to recent reports of extraordinarily high prices being paid by the armed services for simple tools and other parts.
The Democratic Party platform promises to inject more long-range planning, increased competition, better weapons testing, and ''realistic projections of available resources'' into the development and procurement of arms.
In a congressional hearing this week, it was disclosed that while auditors question some $500 million in defense contractors' public-relations costs each year, much of this amount eventually is paid by the US government because of unclear definitions and ambiguous regulations. Fred Newton, deputy director of the Defense Contract Audit Agency, testified that ''some contractors disperse public-relations costs in general cost accounts such as salaries and wages, supplies, and communications.''
''The problem of defining these costs and establishing the extent of their allowability has never been fully resolved,'' acknowledged Donald Sowle, administrator for federal procurement policy in the White House Office of Management and Budget. In one instance, according to federal records, a defense contractor charged the government for aircraft models, emblems, and golf shirts.
In another legislative hearing this week, government investigators (citing internal corporate documents) charged that General Dynamics Corporation and the company's Electric Boat division purposely underestimated submarine-building costs and subsequently convinced the Navy to pay cost overruns totalling more than $600 million. Company officials vigorously deny the allegations.
Navy Secretary John Lehman has been a persistent critic of defense contractors who do not fulfill their obligations, frequently threatening not to pay them. But he says many of today's new ships are being acquired ''ahead of schedule and under budget.''
Democrats clearly intend to make the most of the weapons-procurement issue in the presidential campaign.
US Rep. Patricia Schroeder (D) of Colorado told several hundred young people at a rally on the steps of the Capitol this week: ''You are the ones who are paying this insane price for these insane weapons.''