President Reagan yesterday sought and received the resignations of two embattled Environmental Protection Agency officials, Inspector General Matthew N. Novick and Assistant Administrator John P. Horton, White House officials reported.

The officials said the resignations are the first volley in a White House effort to make a "fresh start" at the agency following allegations of mismanagement, conflicts of interest and political manipulation of the hazardous waste cleanup program.

The president is expected today to fill the two vacant posts as well as that of Rita M. Lavelle, whom Reagan fired as EPA hazardous waste cleanup program chief on Feb. 7, White House officials said.

The forced resignation of Novick came less than a week after it was disclosed that he had written a critical audit of the $1.6 billion Superfund for toxic waste cleanup. The General Accounting Office is also looking into allegations, which Novick has denied, that he used government employes to do personal work.

The Justice Department is looking into accusations that Horton used his EPA office and an aide to do work for several of his private businesses on government time. Horton has said he did nothing wrong.

Horton told the Associated Press yesterday that he had been asked to resign by Helene von Damm, head of the White House personnel office. "They told me, 'We have a problem and would you be willing to resign to help out?' And I said yes," he was quoted as saying.

The forced resignations were not announced by the White House. But presidential aides who asked not to be identified confirmed them. They said Reagan had not directly demanded the resignations, but his senior staff aides conveyed the requests.

The White House officials stressed that Novick and Horton resigned "without prejudice" and may get other administration posts. "There is no feeling there is any wrongdoing on their part," one White House official said.

Craig Fuller, assistant to the president for Cabinet affairs, said the resignations will allow the administration to "strengthen the management and administration" at the troubled agency.

In a breakfast meeting with reporters yesterday, Reagan said investigations by the Justice Department and the FBI into allegations of wrongdoing at the EPA will help improve the agency's credibility. The president added that "I have not found much substantiation" for the charges.

The forced resignations came after several days of intense debate among senior presidential aides on a strategy for taking command of the damaging EPA controversy. Officials said last night that the resignations were just part of a larger "package" they hoped would blunt the charges that Reagan has given up on environmental protection.

The officials also said the White House wanted to give EPA Administrator Anne M. Burford, whose name was Gorsuch before her marriage last Sunday, new deputies to take stronger control of the agency.

Responding in particular to criticism of the management of the Superfund toxic waste program, the White House is reported ready to nominate Lee Thomas, an official at the Federal Emergency Management Agency, to take Lavelle's job running the hazardous waste cleanup. Thomas helped work out this week's plan to relocate families from dioxin-contaminated Times Beach, Mo.

In addition to filling the vacancies under Burford, the White House was still considering the appointment of a "special legislative counsel" to deal with congressional inquiries, but administration officials said last night it was no longer certain Reagan will take this approach.

White House officials said as of last night Reagan had no plans to seek resignations from any other EPA officials. "The head-rolling is over," one official said.

The forced resignations came under immediate question yesterday by some Democrats investigating the agency. Rep. Mike Synar (D-Okla.) questioned whether Novick, the inspector general, was fired "because he released the audit that revealed gross financial mismanagement and the inability of the agency to account for funds."

Rep. James H. Scheuer (D-N.Y.), chairman of a House science and technology subcommittee, said the president had "made a decision to fire" Novick in a "crude attempt to stem the mushrooming scandal at the EPA."

In her first appearance before a congressional committee since she was fired by Reagan, Lavelle denied on Capitol Hill yesterday that she had done anything "sinister or underhanded." Appearing before the Senate Environment and Public Works Committee, Lavelle denied making "sweetheart deals" with polluters and said that her busy schedule of meetings, including lunches and dinners with industry representatives, was just part of her job.

"Throughout my 10 months at EPA, I was sensitive to the public trust placed in me. My record is a good one and I am proud of it," she said.

In response to questioning, Lavelle criticized the leadership ability of Burford. "We all have strengths, we all have weaknesses. None of them are managers, none have experience in management, and they're insensitive to the need for it."

Lavelle said that Burford was too willing to "to listen to rumors, to encourage runors," and that the EPA was "engulfed in an escalating crisis of name-calling, rumor, criticism, charges and countercharges. The impact of this hasty and disorganized attack on the agency has been to weaken or destroy much of the significant and effective work accomplished in our national effort to clean up the environment."

She complained that she was suspected by Burford and others because she had worked for Reagan when he was governor of California and was believed to have strong White House ties.

"Ever since I arrived, I've been known as a California Reagan plant over at the agency," she said. "I told Mr. Meese it's been more of a millstone than a star on my halo."

Lavelle said she met with or spoke to White House counselor Edwin Meese III or his aide 10 or 12 times during her 10-month tenure, but never to discuss political implications of negotiations.

Lavelle received harsh criticism from several senators because of her practice of allowing members of industries regulated by the EPA to purchase meals for her in some of Washington's fanciest restaurants.

Sen. John H. Chafee, (R-R.I.) charged, "There are allegations of sweetheart deals with the very people who've been wining and dining you. You pursued these people more vigorously in the restaurants than the courts."

Lavelle responded, "That's one observation one could make. Obviously, I do not agree with it. I think my role was to sell industry on an approach . . . . The approach that industry is all bad and government all good was put to rest with Watergate."