The number of high school seniors applying for early action admission to Harvard this year dropped by 9 percent this year mirroring similar trends at Yale and Princeton. Mean while Brown and MIT experienced dramatic increases in applicant numbers.

Ivy League admissions officers yesterday attributed the declines primarily to three factors the shrinking number of 18-year-olds in the country, anxiety about financial aid, and a substantial shift in the concentration of families from the Northeast and New England to the Southwest and Sun Belt states, where they are harder to reach through recruitment.

Fourteen hundred and five students--down from 1545 last year--applied to Harvard under the early action plan, which requires students to file applications for a single school by November 1.

Only five schools--Harvard, Yale, Princeton, Brown and MIT--participate in the arrangement, under which accepted applicants are under no obligation to attend.

Harvard's number of early-action applications has decreased each year since the fall of 1979, the first year in which students were forbidden from applying early to more than one school. But this year's decline of 140 is larger than last year's of about 45. L. Fred Jewett '57, dean of admissions and financial aid, said yesterday.

Jewett said declines in the early action pool often foreshadow a decline in the overall pool. But he added that he would be much more concerned it early returns showed a sharp decrease of interest in one region or it the early applicants turn out to be less talented overall than previous groups.

"A whole range of additional factors" influence early action applicants differently from regular ones. Jewett said, citing students apparent tendency in recent years to apply early to schools where they are more confident of being accepted, such as Brown.

Marcia H. Connolly, associate director of admissions, speculated yesterday that the decline might stem from students' worries about money, but added that the college choices of students who turn Harvard down don't always support that assumption.

"Last year as usual, we lost more to Yale than anywhere else," she said nothing that Yale's financial aid guarantees are virtually identical to Harvard's.

Early in the Day

Margit Dahl director of admissions at Yale College, said yesterday that Yale's drop to 940 early applications from 1158 last year a 19 percent decline does not fully reflect national trends since Yale mailed out it application form 1158 last year--a 19 percent decline--does not fully reflect national trends, since Yale mailed out its application forms too late this fall for many students to apply in time.

But she also noted that financial worries affect equally all the schools experiencing drops, since all have similar and policies. "None of us can afford to buy students. Dahl said.

Other admissions officers thought the drop might portend more of last year's problems in attracting minority and low income students. James Wickenden, dean of admissions at Princeton, said yesterday he was "very pessimistic" about attracting minorities this year Princeton's 6 percent drop follows several years of increasing applicant numbers.

But at Brown University where the early action volume jumped by 33 percent from 1608 last year to 2039 an official and that students don't seem any more nervous than last year about financial matters.

Nancy Rhodes, Brown's associate director of admissions yesterday attributed the increase which continues a trend of several years to general good P R" and student distaste for the curricular requirements gaining new emphasis at many Ivy League colleges including Harvard.

Distribution requirements "just are not popular with the kids." Rhodes said Brown's elective system" has made for a slightly more released impression," she added.

Jewett noted that Brown admissions officers also specifically urge students to apply early, whereas Harvard officials rarely start their recruiting trips until just before the November 1 deadline.

The apparent lack of aid anxiety among Brown applicants also "may, unhappily, mean that kids with severe need aren't applying," Rhodes said.