Based on population trends, California will pick up six U.S. House seats, Texas four and Florida three in congressional reapportionment after the 1990 census, according to projections released yesterday by Election Data Services, a private consulting firm on political redistricting.

EDS President Kimball Brace also told a news conference that Census Bureau population figures for congressional districts show that those with the biggest population losses from 1980 to 1986 are largely Democratic and black.

Brace also said that Virginia, Arizona and Georgia apparently will gain one seat apiece if population trends in effect since 1980 continue through 1990.

He said New York would lose three seats; Illinois, Michigan, Ohio and Pennsylvania two each, and Iowa, Kansas, Massachusetts, West Virginia and Wisconsin one each.

The figures suggest strengthened Sun Belt and western voting power in the House at the expense of the Northeast and Midwest, a trend that has continued since the start of the republic and was accelerated by the recent economic-development surge of the South and attendant population changes.

According to Brace's computer analysis of the Census Bureau's 1986 population figures for each congressional district, 95 districts have lost population since 1980. Of the top 50, virtually all in the Northeast and Midwest, all but six were represented by Democrats.

The greatest Republican loss came in the Peoria, Ill., district of House Minority Leader Robert H. Michel. The greatest loss overall -- 69,960, or 13.6 percent -- was in Michigan's 13th District, represented by George Crockett (D).

Brace said census figures show that, of the 21 districts with a population in 1980 more than 40 percent black, 16 lost population. All 21 are represented by Democrats, all of whom are black except Lindy Boggs (La.) and Robert Garcia (N.Y.).

However, of 37 districts with at least 20 percent Hispanic population, all but four gained population, he said.

According to Brace's calculations, while all of Maryland's eight districts had about the same populations after the last census, four have since grown relatively rapidly, while the others have either grown more slowly or lost population.

The fast-growth areas are the districts of Constance A. Morella (R), Roy Dyson (D), Beverly B. Byron (D) and C. Thomas McMillen (D). That means that in 1991, parts of those districts may have to be changed to return all of them to equal size. The other four districts may have to be expanded or reshaped to bring them up in population.

In Virginia, five districts have grown rapidly -- those represented by Herbert H. Bateman (R), Owen B. Pickett (D), D. French Slaughter Jr. (R) and northern Virginia's Frank R. Wolf (R) and Stan Parris (R). The other five have grown slowly.

Changes will be needed to equalize the districts and accommodate addition of an 11th district projected by Brace.

The District of Columbia, which has only one seat and a fixed boundary, will be unaffected.