Ailing Defense Minister Dmitri Ustinov was absent but Mikhail Gorbachov moved to the front row of the Soviet leadership today as the Supreme Soviet, the nation's nominal parliament, met and approved a 12 percent increase in Soviet defense spending.

Gorbachov, at 53 the Politburo's youngest member, has been steadily moving up in leadership lineups since the summer, although there had been some speculation among Soviet-watchers in recent weeks that his position may have been less secure than originally thought.

His rise to the front row at the Supreme Soviet -- with Foreign Minister Andrei Gromyko, Premier Nicolai Tikhonov and President Konstantin Chernenko -- appears to indicate that he is well entrenched in the top leadership ranks and is a strong candidate to succeed Chernenko, who is 73.

Ustinov, 76, has been missing from public view since Sept. 27 and is said to be seriously ill.

The increase in the announced defense budget -- from about $20.5 billion to about $23 billion -- was signaled by Chernenko in a speech Nov. 16, but he had given no figures. While western analysts consider Soviet defense budget figures highly misleading, the mere mention of a priority for the military was an unusual public acknowledgment by the Soviets.

Since the late 1960s, the Soviet budget has shown defense spending at about 17 billion rubles ($20.5 billion) -- a fraction of what western analysts estimate as the true cost of supporting the Soviet military machine. For the last four years, the figure has held firm at 17.05 billion rubles.

Next year's budget shows the figure jumping to 19.063 billion rubles ($23 billion), but diplomats say they consider the new sum no more realistic than the old one.

"The Soviet Union does not seek military superiority, but it will not allow the military-strategic equilibrium to be upset," said Finance Minister Vasily Garbuzov.

The announced boost for the military comes as the Soviets explore new arms talks with the United States. One western diplomat said it could be a signal that, if necessary, the Soviets will not balk at the cost of maintaining a strong defense.

This year the traditional two-day parliamentary session met without the benefit of instructions from the Communist Party Central Committee, the first time in more than 20 years that a Central Committee meeting did not immediately precede a Supreme Soviet session, but there was no explanation for the break in tradition.

Some diplomats speculated that a Central Committee meeting in October may have obviated the need for another. Others said Chernenko's speech on Nov. 16, which dealt with the budget, may have made the meeting unnecessary.

The 1985 budget calls for a spending level of 391.5 billion rubles ($473.7 billion). The predicted growth rate in national income -- roughly equivalent to gross national product -- only slightly exceeds this year's anticipated 3.1 percent.

State Planning Committee Chairman Nikolai Baibakov said this year's growth in industrial output is expected to reach 4.4 percent, exceeding the 4.1 percent target -- the second year of modest growth, following two years of economic slowdown.

Baibakov indicated that oil production fell below target this year but it is expected to rise slightly in 1985, and that natural gas, a star performer in the Soviet economy, is expected to increase 8 percent next year.

Baibakov chastised several ministries for waste and mismanagement and urged better use of technology and resources in meeting goals in 1985.