WASHINGTON (AP) _ Latrines on Navy ships and Air Force planes are taking on the look of the executive washroom, congressional investigators say.

Cover assembly for toilets on the Air Force's C-5B transport aircraft - $1,868. Urinal for a Navy minesweeper - $641. Rubber gaskets to seal drainage holes on airborne toilet systems - $67.50 each.

Tales of overpriced porcelain and rich rubber are only the latest from investigators who uncovered the recent Pentagon acquisitions of $999 pliers and $117 soap dish covers.

Two Republican senators, Charles Grassley of Iowa and William Roth of Delaware, have called for an audit to determine whether the overpricing and system problems ''are as prevalent today as they were in the mid-1980s.''

The Pentagon's inspector general, Susan J. Crawford, has promised to conduct an investigation.

In the meantime, money seems to be going down the toilet.

The government in October 1988 purchased two urinals priced at $641.25 each from a Fairfield, N.J., company, Williams & Watts Inc., according to documents obtained by The Associated Press from investigators.

The purchasing trail for the urinals extended to several companies. Williams & Watts bought the urinals from Chamberlain Manufacturing Co., Gard Division, of Niles, Ill., for $475 apiece. Chamberlain told investigators they purchased the urinals from Paul Supply for $281. Paul Supply said they paid $150 each to Crane/Fiat for the urinals.

Investigators, who questioned a Crane representative on why the company does not sell directly to the government, was told, ''That's how the game is played.''

A program manager for Williams & Watts said the company examined government procurement history files and found that Chamberlain is ''the only known and approved source of supply of this product.'' Scott Adler said his company, which serves as the dealer for Chamberlain, believed the company was the actual manufacturer.

According to Adler, Chamberlain sought to meet the strict military requirements for the urinals, which included shock and vibration tests. The Navy also requires that since the urinals will be on minesweepers, they be non-magnetic. The urinals are made of porcelain with brass valves.

Adler confirmed that his company paid $475 to Chamberlain for the urinals and then sold them to the government for $641, a markup of 35 percent that included various company expenses.

An official at Chamberlain said the person designated to comment, Dr. William Byrne, was unavailable.

Investigators also discovered that in 1984, Chamberlain sold nine of the same urinals directly to the government for $180 each.

The Air Force purchased the toilet cover assembly, a steel-reinforced plastic sheet that covers the top of the toilet, for a price of $1,868.15, investigators said.

The cover, which is manufactured by Weber Aircraft, is 34 inches by 28 inches and two are usually installed on C-5B transport aircraft.

Investigators also found that the government bought four of the drain valve seals at a cost of $67.50 each for use on airborne toilet systems in military aircraft.

The seals are rubber gaskets which are used between a drainage hole and the plug which covers it in toilets.