Under pressure from the nation's medical schools, the Reagan administration has adopted a more flexible collection standard than it originally proposed for the largest federal loan program exclusively for medical students.

But the standard still is so stringent that most of the schools are expected to have trouble meeting it, fueling charges that the administration is attempting to dismantle the $246 million program that was created in 1965 to help needy students, especially minorities.

Based on 1982 figures, 79 of the nation's 125 accredited medical schools would not be able to meet the standard. Students attending schools that cannot achieve the standard would be unable to qualify for new loans.

Locally, Howard University's College of Medicine has the worst collection rate in the nation for the so-called health professions student loan (HPSL) program: eight times the rate that would be allowed under the new regulations. Three other area medical schools, as well as Harvard University's, also had higher delinquency rates last year than would be permitted now.

Under the new rules, which take effect immediately, schools are supposed to lower delinquency rates by the end of this month to 5 percent of all dollars owed.

Schools that cannot meet that standard immediately must cut their delinquency rates by 50 percent within six months and continue cutting them in half over each succeeding six-month period until they achieve the 5 percent rate.

If they fall behind in meeting the goal, they can make no new loans.

And if after another six months the schools still fail to meet the target, they will be dropped from the program.

The Health and Human Services Department originally wanted to cut all medical schools that did not achieve the 5 percent rate by March 31. It said that rate was realistic because it was more liberal than the 3 percent delinquency rate that most commercial lending institutions expect when they make loans to highly paid professionals such as doctors. The HPSL loans are interest-free and not due until after a student leaves school.

But the Association of American Medical Colleges, which represents all accredited medical schools, said that level was unfair because the loans are made to students with "exceptional financial needs." Loans to these students are much riskier than loans to established professionals, it reasoned.

After receiving more than 152 comments, 132 of which were negative, HHS modified its plan.

Since the administration began its crackdown on federal debtors in 1981, medical schools have made substantial progress in reducing delinquency rates, HHS said.

The number of HPSL borrowers who were at least 91 days late in repaying loans dropped from 11.8 percent in 1981 to 8.7 percent in 1982, according to the department.

Yet despite such progress, the majority of U.S. medical schools had delinquency rates higher than 5 percent last year.

Howard cut its delinquency rate by one-third in 1982, but the school still reported a 40.9 percent delinquency rate for the period ended June 30, 1982, the most recent figures available.

The Medical College of Virginia at Virginia Commonwealth University reported a delinquency rate of 14 percent in June, 1982, compared with 22.05 percent in 1981.

The University of Virginia Medical School had a 6.12 percent rate last year compared with 11.1 percent in 1981.

The University of Maryland Medical School in Baltimore reported a 6.47 percent deliquency rate in 1982. Its 1981 figure is unavailable.

Georgetown Medical School cut its delinquency rate from 3.6 percent in 1981 to 2.97 last year; Eastern Virginia Medical School dropped its rate from 13.89 to 1.1 percent, and Johns Hopkins University Medical School dropped its rate from 5.2 percent in 1981 to 3.02 last year, HHS said.

Sterling Lloyd, an assistant dean at Howard University's medical school, said approximately 35 percent of its students received loans totaling $232,250 in the 1981-82 academic year.

Lloyd said students would be forced to apply for much more expensive loans if the school were dropped from the program.