Officials of the Defense Department, which is spending about $400 million on overtime pay this year, told a congressional subcommittee yesterday that they cannot say how many of their employes are collecting such pay or what kind of work is being performed to earn it.

Carl W. Clewlow, a Defense personnel official, told yesterday's hearing on federal overtime pay practices that managers at defense, the government's largest employer, "never saw the need" to compile as much detailed information on overtime payments as congressional investigators had requested.

Because of Denfense's sheer size and its efforts to decentralize decision-making authority, such information is collected only at far-flung installations around the world and sent only in general form to top managers in Washington, Clewlow said.

Rep. Gladys Noon Spellman (D-Md.), who chairs the subcommittee on compensation and employe benefits, expressed amazement at Defense claims that such information would have to be gathered manually, and that the job would take three months and cost $100, 000. She noted that other large and less technology oriented agencies had managed to supply such information.

In a sometime ssharp exchange, Spellman told Defense officials she was puzzled about how they arrived at a budget request figure when they seemed to lack a rationale for it. She also waved a stack of reports on internal audits conducted by Defense and said the documents "do not bear out" officials' claims that they are doing all they can to improve their accounting systems and managerial control of payments.

The Defense Department has 137 different accounting systems, 15 of which relate to civilian payrolls, according to testimony. Of the 15, only 10 have been approved by General Accounting Office as required under a 1950 law.

Defense officials noted that four of the unapproved systems were added recently and that the fifth is awaiting GAO approval.

Defense could save millions of dollars, especially in foreign military sales, if it upgraded its accounting systems to meet GAO recommendations, GAO investigators said.

Yesterday's hearing was the subcommittee's second on federal overtime pay policies. Congressional investigators have charged that the government's overtime pay systems have become so poorly managed and confused that they encourage waste, abuse and fraud.

In the highest category of overtime income, about 1,000 federal workers collected approximately $12 million in overtime pay - or an average of four hours apiece for each working day - in a recent one-year period, according to information supplied thus far by agencies.

Indignant officials of the Department of Housing and Urban Development said yesterday that congressional investigators had made "misleading and damaging" statements about the presence of the cartoon character, Donald Duck, on the HUD payroll. Those statements, the officials said, "put us on the funny pages all across America."

In what the subcommittee had dubbed "The Walt Disney affair," GAO investigators had managed to slip Donald Duck and 29 other Disney cartoon characters, including Mickey and Minnie Mouse, into HUD payroll computers. The investigators said they persuaded the computer to issue them checks for as much as $99,000, a maneuver that the computer should have rejected, according to last week's testimony.

That GAO test occurred before the present administration took office and did not produce an actual check for Donald Duck. HUD's William A. Medina said yesterday. He said major deficiencies that permitted the test to go as far as it did have been corrected.

GAO officials expressed regret yesterday that the 1975 date of the Donald Duck report had not been mentioned in the earlier hearing. "There was no intention to obscure this point," GAO official Donald I. Sentlebury said.

But he and others insisted that these clarifications do not alter the point of the incident - that government payroll procedures need to be tightened and monitored constantly. The same deception might work on any number of existing systems today, they said.

HUD officials also noted that they cut employe overtime hours last year by 70 percent and plan to do better this year. They did this through "significantly better management," they said.

For example, employes who work at a substandard pace no loner may work overtime, they said.

Still, 87 HUD employes collected at least six months worth of overtime during the last one-year period, and 480 others collected between three and six months' worth. HUD officials said that was the result of emergency work in connection with disasters, such as floods.

Congressional investigators said yesterday that they also are looking into charges made by federal employes that:

General Service Administration managers urged employes in 1977 to work unnecessary overtime so $23,000 left in the overtime budget would be used and the next year's appropriation would not be lowered.

Other federal employes have been forced to work overtime without compensation require by law.

An Army Corps of Engineers unit requested an authorization for overtime 12 years ago for an" emergency" and still uses that to justify overtime payments.

State Department officials confirmed yesterday that their armed security agents are working such long hours that their health and the safety of their charges are being jeopardized. State is attempting to correct to problem, the officials said.

Justice Department officials said they "had not been aware of the numbers" concerning overtime payments to immigration inspectors under a 1931 law. They are "looking into it," the officials said.