Undated (AP) _ Grain and soybean futures prices were mixed to sharply lower Tuesday after a bearish U.S. Department of Agriculture crop report pushed the markets into a corner and kept them in a defensive posture the entire day.

It was the second straight session that the USDA report, issued after the close of trading Monday, exerted pressure on the grains.

In other markets, many of them affected by a Veterans Day Holiday-thinned corps of traders, livestock and meat futures climbed higher, petroleum futures continued a move upward, and precious metals turned in a mixed performance.

The USDA report showed the department underestimated the Soviet Union's domestic production by at least 15 million tons. That means the Soviets will be shopping for about 6 million fewer tons of grain than had been expected.

Neither number caught traders entirely by surprise, however.

''The grains look like they're where they belong,'' said Steve Remsing of Jack Carl Associates, Inc. in Chicago. ''We've been in a 20-cent trading range for a while because of this and it will take something more drastic to change that.''

Wheat took the biggest hit as a result of the USDA report.

Both corn and soybeans fared slightly better because of low trading volumes, light overnight deliveries, and tender offers from South Korea and Brazil.

Oats concluded a second rallying session on the strength of a poor 1986 crop.

At the Chicago Board of Trade, wheat settled 1/4 cent to 5 1/4 cents lower, with the contract for delivery in December at $2.77 1/2 a bushel; corn was 1 1/4 cents to 2 1/4 cents lower, with December at $1.70 1/2 a bushel; oats were 1/2 cent lower to 2 3/4 cents higher, with December at $1.51 3/4 a bushel; and soybeans were 3 1/2 cents lower to 2 1/2 cents higher, with November at $4.98 1/4 a bushel.

Lower feedlot estimates for cattle and meatpackers willing to pay top dollars for hogs in recent days translated into strong performances at the Chicago Mercantile Exchange.

''We're estimating the numbers farmers placed on feedlot will be 10 percent lower than last year, which reverses a three-month trend,'' said Chuck Levitt of Shearson Lehman Bros. in Chicago.

Live cattle were .07 cent to .50 cent higher, with December at 60.82 cents a pound; feeder cattle were unchanged to .30 cent higher, with November at 62.32 cents a pound; live hogs were .10 cent to .57 cent higher, with December at 53.27 cents a pound; and frozen pork bellies were .95 cent to 1.55 cents higher, with February at 67.35 cents a pound.

Petroleum futures prices continued a quiet, but steady move upward begun almost two weeks ago when Saudi Arabia signaled its willingess to cooperate on a higher pricing schedule by firing oil chief Ahmed Zaki Yamani.

Many traders remained on the sidelines again Tuesday and at the American Petroleum Institute meetings in Houston. The petroleum market also tried to anticipate a second, more important meeting scheduled Friday for Ecuador, where OPEC's oil-pricing committee is scheduled to convene.

At the New York Mercantile Exchange, crude oil settled 6 cents to26 cents higher, with December at $15.40 a barrel; heating oil was .25 cent lower to .56 cent higher, with December at 44.37 cents a gallon; and unleaded gasoline was .24 cent to .70 cent higher, with December at 41.87 cents a gallon.

Precious metals performed in mixed fashion.

At the New York Mercantile Exchange, platinum settled $9.70 to $10.20 lower, with November at $536.20 a troy ounce.

At the New York Commodity Exchange, gold settled $1.60 to $1.80 higher with November at $408.10 a troy ounce; and silver was 2 cents to 2.8 cents higher with November at 576.2 cents a troy ounce.