CLASSICAL music of the modern era, so often characterized by dissonance and complexity, has always tended to provoke resistance as well as enthusiasm. In championing the cause, therefore, a certain amount of evangelical zeal is almost a prerequisite. Around and about Washington, few are as generously endowed with this traits as Tony Ames, producing director of the 20th Century Consort.

"Frankly," says Ames, "we're out to show the public that modern music can be fun - and not only fun, but accessible, exciting and moving."

It is just this liberated approach that is the distinctive calling card of the consort, which, now in its third year, is about to move into an important, new and more visible phase of activity.

Just named a "resident" performing group by the Smithsonian's Division of Performing Arts, the consort will shift in the 1978-79 season to the Hirshhorn out-of-city tours and other innovative undertakings.

The consort's outreach philosophy is a response to a major dilemma of 20th century music - the chasm between composer and audience that opened up with the revolutionary changes in musical syntax at the time of Schoenberg's "Pierrot Lumaire" (1912) and Stravinsky's "Rite of Spring" (1913) and still has yet to be successfully bridged on a large scale.

The consort attempts to cope with the problem not by ignoring it, but by trying to take its measure and gauge its effect. As Christopher Kendall, artistic director and conductor of the consort, puts it:

"Let's face it, contemporary music is sort of a wreck. In the present century, a substantial schism has developed between composers of new music and the potential audience for that music. Over the last couple of decades, composers have been writing in a myriad of styles, but by and large most of the music falls into one of two categories.

"On the one hand, there is music which, while perfectly valid from an artistic standpoint, doesn't seek to grapple with the problems of contemporary musical language - it hasn't faced up to the crisis. I'm thinking of the so-called "conservative" music of people like Menotti, Barber or Irving Fine.

"On the other hand, there is the music - and most of the serial, post-serial and aleatoric music of recent times fits here - which has simply rejected communication with an audience as a valid esthetic criterion."

The consort refuses to play any one side of the fence. "In our consort programs," says Kendall, "we don't reject any category." A perusal of the group's repetoire over the past several seasons confirms this catholicity of approach, ranging from Debussy, Ravel, Bartok and Milhaud to Lutoslawski, Davidovsky, Berio and Gerhard.

For the consort, the key word is "balance," the guiding concept of its programming strategy. Kendall and his associates do feel there are recent encouraging signs of a "music of reconciliation," a new desire on the part of composers to involve listeners beyond the hard-core contemporary music buffs.

As Tony Ames puts it, "Many composers today are beginning to reevaluate the priorities on which their music is based, with a new eye toward large-scale-communication."

Kendal concurs. "George Rochberg's recent music, for example - apart from the question of whether it succeeds - is well-composed, in the tradition of fine craftsmanship, but it also has a decidedly emotional impact on audiences. George Crumb is another obvious example. In his own very personal way, he writes music that has integrity from a contemporary viewpoint, but it can also reach people."

The consort, however, tries not to play favorites, or to emphasize any one school or direction. "Our main aim," says Kendall, "is to provide a well-balanced listening experience for the audience, by embracing both challenging and more accessible repetoire." By the same token, says Ames, "We hope to bring the Washington scene a more balanced view of the range of today's music than groups that restrict themselves to one school or another."

In these respects and others, the consort tries to stake out a median position between what it considers the extreme approaches cultivated elsewhere. There are some groups, like the Contemporary Music Forum locally, that pursue a more aggressively contemporary policy, stressing new work, often radical in idiom, frequently by local composers. There's a need for this type of crusading, the consort feels, but it tends to attract limited circles of hearers already sworn to the cause.

There are other groups exemplified locally by the splendid Theater Chamber Players, which emphasize the broader historical spectrum of chamber music as a whole, and try to foster appreciation of modern music by letting it be heard against a traditional perspective.

The consort, Ames and Kendall feel, occupies a middle ground between these two. Unlike the TCP, the consort draws its programs exclusively from the 20th century. Unlike the Forum, the consort tackles all corners of the modern repertoire, old and new, accessible and difficult. There are indications this tack pays off in terms of audience appeal. By the end of the 1977 season, the consort had established an average attendence of 500 - a remarkable figure for the contemporary field, and more than respectable in the general realm of chamber music.

The consort was founded in 1975 when conductor Kendall met Ames, principal percussionist of the National Symphony and the two discovered their common interest in 20th-century music.

After two years of free concerts around Washington, and the just-concluded third season at the Marvin Theater, the group invited by James Morris of Smithsonian's Division of Performing Arts to take up residence at the Hirshhorn Museum's auditorium for the 1978-79 season beginning next fall.

Under the Smithsonian banner, two recordings are in the works, as pilots for an ambitious series perhaps along the lines of the Smithsonian's very successful jazz anthology. There's also a large possibility that the Emerson String Quartet, recent co-recipient of the Naumburg Chamber Music Award, will join the consort's core of about a dozen musicians as regular participants in consort events.

Both Ames and Kendall exude a sense of optimism and anticipation towards the future, as well they might, given the enhanced outlook for coming seasons. At the same time, maturity brings not only added privileges but also responsibilities, and it's clear that the consort will have its hand full trying to live up to its newly elevated status and scope. CAPTION: Picture 1, The 20th Century Consort: Liberated and innovative musicians, but can they bridge "the schism that has developed between the composers of modern music and the potential audience for their music?"; Picture 2, Tony Ames: Evangelical zeal.