MOSCOW, SEPT. 28 -- Excessive Soviet secrecy about military spending and preparedness is outdated in the new era of openness, according to two Soviet commentators writing in journals published this week.

The challenge for more complete facts and figures from the powerful Ministry of Defense comes after Soviet leader Mikhail Gorbachev, in an article published Sept. 17, promised to do "more work" on providing comparable defense figures as a way of building trust between East and West.

"I think that given proper effort . . . within the next two or three years, we will be able to compare the figures that are of interest to us and our partners," Gorbachev wrote in an article published in the Communist Party newspaper Pravda.

Soviet intentions to lift, at least partially, the cloak of secrecy that has traditionally surrounded its defense establishment were confirmed in an article that appeared in the weekly Moscow News earlier this month. There, commentator Viktor Zoppi said the Soviet Union is prepared to publish "not only the budget figures directly connected with expenditures by the U.S.S.R. Defense Ministry, but also those that are connected with the financing of the R and D {research and development} work and with the purchase of arms and military hardware."

The Soviet budget every year reflects a figure for defense spending that western analysts view as grossly understated. The figure, which remained unchanged during the years of Soviet military buildup, went up slightly recently, reaching 20.2 billion rubles -- about $32.3 billion at the official rate -- or 4.6 percent of total state spending in 1987.

Writing in this month's Communist Party journal Kommunist, Stanislav Kondrashov, a well-known international commentator for the government newspaper Izvestia, said the lack of "necessary information about military and military-political affairs" hampers Soviet journalists in their work.

"It is no secret that some of our military secrets, touching on the number and military characteristics of various nuclear missiles, have not been a secret for a long time abroad, thanks to space and electronic intelligence," he wrote.

Pyotr Cherkasov, in a book review in the journal Novy Mir, complained that Soviet diplomats, experts and international commentators must rely on military figures published in western publications.