The Soviets, in a tough retaliation Saturday for a second round of diplomatic expulsions by Canada on spy charges, expelled a defense attache and told 25 Russian staff members not to report for work at the Canadian Embassy.

The Soviets also barred from re-entering the country seven other Canadian diplomats who had not served in Moscow for at least the last two years.The ban on work by half the Soviet staff will likely leave the embassy without drivers, secretaries, janitors and other workers who perform routine tasks and will make everyday life much more difficult for the remaining Canadian diplomats.

Canada struck the first blow in the expulsion war 10 days ago with allegations from Ottawa that the Soviets were conducting industrial espionage. In two rounds of expulsions, the Canadian government kicked out eight Russian diplomats and said 11 others not now in the country could not return.

The abrupt Soviet action Saturday raised to 13 the number of Canadian diplomats barred in retaliatory action. Three have been expelled outright and 10 who previously served in Moscow will not be allowed to return.

The official Tass news agency reported Saturday that in the latest expulsion, Col. Larry Bowen, the defense attache, was ordered home, and said seven other diplomats will not be allowed to return.

Canada's ambassador in Moscow, Vernon G. Turner, was summoned Friday by the Deputy Minister of Foreign Affairs Alexander Bessmertnykh and informed of the new actions, Tass said.

In Ottawa, a spokesman for the External Affairs Department said the government "has no comment at all," but added there may be a statement later Saturday.

A White House spokesman said the Reagan administration also had no reaction.