The Reagan administration has urged Mitch Snyder, advocate for the homeless, not to continue delaying General Services Administration workers from beginning renovation of a shelter for the homeless in Northwest Washington.

Snyder had refused last week to move out several hundred residents to allow the renovations to begin.

In a letter to Snyder, Charles Baker, undersecretary of the U.S. Department of Health and Human Services, asked Snyder on Wednesday to make way for the workers and said that the work must begin soon in order to complete the repairs by winter.

Snyder, who heads the Community for Creative Non-Violence, responded by sending a letter to Health and Human Services Secretary Margaret M. Heckler yesterday asking the government to make emergency repairs to the shelter and repeating his demand that the government produce architectural renderings of its proposed renovation of the facility.

If the government fails to do so, Snyder said in his letter, the Community for Creative Non-Violence will turn responsibility for the shelter and its residents over to the federal government. He said that his organization is prepared to file a suit to enforce the turnover.

President Reagan authorized renovating the shelter at 425 Second St. NW last fall, ending a 51-day hunger strike by Snyder. Since then, the activist and the government have disagreed over how much renovation is required to make the facility a model shelter.

Snyder said he believes the GSA renovation will amount to a "patch job" and that he wants the government to put its plans on paper so he can see if it is living up to the "physical model shelter" promised in a statement by Heckler last fall.

Snyder said his concern is that the government is not prepared to spend enough money to do the job properly and that his organization will be saddled with operating an inadequate structure, a federal building that was turned over to the organization after Snyder's hunger strike.

"What's got us climbing the walls is that these folks are spending . . . $900 for ashtrays," he said, referring to a highly publicized component produced by a military contractor, "and we get them coming to our building trying to patch up a thing that is literally falling down on 700 people a night."

Baker said in his letter, however, that the GSA has assured him that, under its current renovation plans, "if normal repair and maintenance is accomplished each year, the facility will serve for as long as necessary."

Baker added in an interview, "I am completely confident of their [GSA's] commitment and ability to do this job . . . . If we go through a lot of nit-picking and one thing and another and wind up delaying this extensively, we are going to see snow on the ground before this thing is done, and I won't have that."

Baker said that he would like to meet with Snyder on Monday to clarify the details of the GSA renovation and resolve the dispute.