U.S. District Court Judge Charles R. Richey yesterday said he will hear complete legal agruments on Feb. 25 in connection with challenges to President Reagan's retroactive job hiring freeze.

In the meantime, Richey extended for 10 days another judge's order that temporarily reinstated three persons who had reported for duty with the U.S. Customs Service but were informed they were out of a job because of the freeze.

Four different cases involving the hiring freeze are now before Richey, including lawsuits brought by the National Treasury Employees Union and the National Association of Government Employees. Richey is expected to consolidate the legal questions in all those cases that center on Reagan's authority to rescind job offers made after Nov. 4, election day. The job freeze was Reagan's first official act as president.

The freeze, which prohibits government agencies from hiring additional employes after Jan. 20, Inauguration Day, also affects persons who received job commitment letters after Nov. 4 but had not started work by Inauguration Day. The three employes, who were reinstated in their jobs by another federal judge in Washington Feb. 6, had showed up for work on Jan. 26.

That narrow ruling by Judge John Pratt was seen as an important step for opponents of the retroactive job freeze, which abruptly cut off employment for thousands of new hires. But Richey yesterday postponed ruling on whether to expand the scope of the lawsuits to include all persons who lost their jobs as a result of the hiring freeze.

The government contends that those persons had received only offers of employment in commitment letters and not actual appointments to those jobs. Without formal apointment by an authorized federal official, through what is known as a "Standard Form 50," those persons could legally be deprived of their jobs through the retroactive hiring freeze, the government argues.

Attorneys for the new hires contend that the form, which states the employe's job title, grade and pay and is placed in a personnel folder, is merely a formality that follows after an employe has been chosen for -- and thus appointed to fill -- a job. Those attorneys argue that the government cannot withdraw such appointments without first giving the employe adequate notice and an opportunity to respond to the termination decision.