Mary Treadwell's defense lawyers concluded their case yesterday at her fraud and conspiracy trial after presenting testimony that the federal government lost more money when it assumed control of the dilapidated Clifton Terrace apartment complex in 1978 than in any year that Treadwell's firm owned it.

One of the prosecutors in the case, Assistant U.S. Attorney William D. Pease, said there is a "very strong likelihood" that, starting this morning, the government will present some rebuttal testimony in the complex case, but that no decision had been made.

U.S. District Judge John Garrett Penn sent the jury of eight women and four men home for the day at midafternoon after they heard brief testimony from the last two of 17 defense witnesses. It now appears that the jury could start its consideration of the case by early next week.

Treadwell's chief court-appointed attorney, John W. Nields, has tried repeatedly during the five-week-old trial to cast blame on the Department of Housing and Urban Development and other officials at P.I. Properties Inc., the now-defunct real estate firm Treadwell headed, for the financial and management problems the company encountered in owning and operating the slum-like, 285-unit Clifton Terrace project.

Yesterday, he tried to show that HUD actually fared worse than P.I. Properties in operating the Northwest Washington apartment complex.

S. Daniel Raley, a deputy director in the Washington-area office of the Department of Housing and Urban Development, testified that from late August 1978, when HUD foreclosed on P.I. Properties' largely unpaid mortgage on Clifton Terrace, until Sept. 8, 1979, the federal agency lost $584,205 at the complex.

P.I. Properties managed the project for HUD for 15 months in 1974 and 1975 and then owned and operated Clifton Terrace from mid-1975 until the federal agency foreclosed. During that time, P.I. Properties' annual losses averaged between $100,000 and $150,000, according to earlier testimony.

Nields had sought to introduce evidence showing that HUD's substantial losses continued until the past few weeks, when HUD again sold the project, while prosecutors in the case tried to keep Raley from testifying altogether. Penn struck a middle ground, allowing Raley to testify about the loss in the year after HUD foreclosed on the P.I. Properties' mortgage.

Treadwell is accused of using P.I. Properties to defraud the federal government and Clifton Terrace's impoverished tenants of thousands of dollars to enrich herself. In addition to fraud and conspiracy, she is accused of tax evasion and making false statements to federal officials.

In about 13 hours of testimony last week, Treadwell acknowledged that she had made mistakes in owning and operating Clifton Terrace, but denied that she ever took any money from the complex's operating account for her own use or for that of her various other business ventures. She acknowledged that she did not file 1976-78 federal income-tax returns until 1980 and that during the 1976-78 period she paid only $18,800 in federal taxes. The government has charged her with evading $33,000 in taxes during the three-year period.

Treadwell accused Robert E. Lee, P.I. Properties' former general manager, of numerous improprieties before she fired him in 1977, and to a lesser degree blamed her sister, Joan M. Booth, Clifton Terrace's project manager, for various misdeeds. Both Lee and Booth have already pleaded guilty to conspiracy and other charges in the case. Neither has been called as a witness in the case, although Lee may be called today by the government as a rebuttal witness against Treadwell.

Charles W. Rinker Jr., another former P.I. Properties official and the only person charged and then cleared of criminal wrongdoing in the case, testified that Booth, during a chance conversation he had with her in 1982, said "that Mary and I were the only innocent parties in the case."

The key accusations against Treadwell came during 12 hours of testimony by Zellene Laney, P.I. Properties' former bookkeeper, who along with others testified that Treadwell regularly tapped Clifton Terrace's operating account or the security deposits of tenants to pay personal bills and to provide collateral for loans and money to invest in various Treadwell-run ventures.