President Reagan yesterday rejected a plan devised by a federal agency to forcibly evict hundreds of residents of a controversial downtown Washington shelter for the homeless operated by the Community for Creative Non-Violence, according to the White House.

The decision came a day after a top official of the Department of Health and Human Services, C. McClain Haddow, said residents of the shelter at 425 Second St. NW, which is operating in defiance of a federal order, would be evicted "in a few days."

The president's decision, which capped a day of conflicting policy statements by the White House and Haddow, nullified a plan described by Haddow to use agents of the Federal Protection and Safety Division of the General Services Administration to assault the CCNV shelter. Some of those agents previously entered the fortified shelter undercover to assess whether residents were armed or otherwise preparing to fight eviction, according to Haddow, a former HHS chief of staff and an agency spokesman on the shelter issue.

"We do not want to provoke violence," said White House spokesman Albert R. (Rusty) Brashear, who said Reagan had reviewed the shelter problem yesterday afternoon in California. "We have no plans to evict anyone at this time."

Reagan first entered the highly charged homeless controversy on the eve of the 1984 election, when he persuaded CCNV leader Mitch Snyder to abandon his 51-day hunger strike by pledging to provide funds to refurbish the Second Street shelter to create a "model physical shelter." HHS officials later withdrew the offer, after months of bickering with Snyder. Snyder has accused the president of breaking his word with the homeless.

"I'm very, very encouraged," Snyder said yesterday. "It's good news . . . . We've been living on the edge for weeks now."

Snyder said he believes the White House's decision not to close the center immediately means that D.C. government officials will honor an offer to spend up to $300,000 to patch holes in the roof and fix windows, toilets, sinks and other facilities.

Snyder said city officials had offered weeks ago to spend the money to "winterize" the building if federal officials indicated they would not shut down the shelter immediately.

He charged that Haddow and his associates, who repeatedly clashed with Snyder and other CCNV leaders, were obstacles to resolving the impasse.

"The stumbling block may have been removed," he said. "We've been trying very hard to get the White House into this situation because we hoped they would deal with it more rationally."

Brashear said the administration's policy was to persuade residents of the shelter gradually to leave the rundown facility and take up lodging at one of two shelters the federal government opened last month in Anacostia, or at other city and private shelters throughout the District.

Brashear's comments contradicted remarks made Friday by Haddow that the shelter would be closed "in a few days."

Haddow said yesterday that the White House has "no idea of the status of the planning" to shut down the shelter, which has been kept open by CCNV despite an adverse U.S. District Court ruling that the building is an unfit place to live and an eviction notice that was posted by HHS.

Haddow, 35, who was chief of staff to Health and Human Services Secretary Margaret Heckler for two years, said he was designated as the agency spokesman on the homeless issue by the newly appointed HHS secretary, Otis R. Bowen. Haddow, who currently serves as acting administrator of the agency's health care financing administration, took a leading role in the department's affairs during the the transition period after Heckler's appointment as ambassador to Ireland.

He said he intends to leave the department Feb. 1 to open a management consulting business in Washington.

Thomas R. Burke, the new acting chief of staff at HHS, said yesterday he has been designated as the department's new spokesman on the shelter issue.

" Closing the shelter is not imminent, and I'm going to have to talk to Mac Haddow ," Burke said. He added there is no timetable for evicting residents of the shelter. "We're still discussing it."

Asked if the plans for eviction and the resultant confusion yesterday would damage any careers at HHS, Burke replied, "Nobody wants to put any personnel notices out during the holiday season."

Informed of Reagan's decision, Haddow said, "I'm sure there will be discussions about it. I'm sure that the president doesn't want for those homeless people to be in a position where their lives are threatened by fire every night . . . . Once he is made aware of that fact it will play into his final decision."

In an interview yesterday, Haddow spelled out his department's plan for closing down the shelter, which he said involved the use of highly trained Federal Protection agents, backed up by D.C. police officers.

Haddow said the federal agents had been specially trained to enter the Second Street building and evict its residents, by force if necessary.

"It's not our choosing," said Haddow, "but what do you do if you get someone in there with a tommy gun? We have to treat this as a worst-case scenario."

D.C. Mayor Marion Barry, who attempted for much of the year to steer clear of the controversy over the CCNV shelter, said repeatedly that city police officers would not take part in any effort to evict homeless persons. However, Police Chief Maurice T. Turner Jr. confirmed yesterday that his department had conferred with HHS officials and agreed to have officers on hand during an eviction in case of violence.

Haddow said the undercover Federal Protection agents who infiltrated the shelter had found weapons, including firearms. Snyder said that some of the residents may have brought guns into the shelter, but that there is not a large cache of weapons.

Turner said he has received no reports that residents of the Second Street shelter are armed.

According to Haddow, many of the shelter residents are Vietnam veterans, whom he called "highly trained people even though they may be mentally infirm." He said some of the veterans "specialized at doing one thing: killing people."

Haddow said he is convinced that violence would be inevitable in the course of an attempted eviction, noting that Snyder "has people bunkered in" the shelter, which has been fortified against a possible assault.

He said the residents of the shelter are "a group of people with mental problems and emotional difficulties" who "could do things that are not in their best interest.

"All of these street people are armed," he said. "You'd have to restrain them. Our people are going through specialized training in order to deal with that kind of person."

Haddow and White House spokesman Brashear disagreed yesterday on which agency will make the final decision on whether and how to evict homeless people from the shelter. Haddow insisted the decision will be made by HHS, which holds the use permit for the dilapidated building.

Brashear said the decision is up to GSA, which technically owns the structure.

The complicated issue of homelessness once again assumed great national importance recently as temperatures plunged with the arrival of winter.

Throughout the country, the bodies of a number of homeless persons have been found this month, apparently victims of the cold. Two men were found dead on Washington streets Thursday morning.

For more than a year, the spotlight in the District has been on the CCNV center, whose fate has been buffeted by the often conflicting agendas of the outspoken Snyder, the White House, federal agencies and city officials.

Reagan, apparently influenced by Snyder's 51-day hunger strike, promised to refurbish the CCNV facility.

In June, Snyder and HHS officials began to bicker over the extent of the renovations that would be financed by the federal government. HHS officials, unable or unwilling to compromise with CCNV, announced plans to close the federally owned shelter and give $3.7 million to another group that advocates homeless rights, the D.C. Coalition for the Homeless, to run a temporary substitute shelter in Anacostia and to map long-range plans for the city's homeless.

Snyder's group filed suit in court seeking to prevent the federal government from closing the shelter, but a federal court judge cleared the way for the eviction by ruling that the building was not a fit place to live.

Temperatures tonight are expected to dip into the upper teens in the metropolitan area, according to the National Weather Service.